As apcyberax stated, there is NO way Virgin would have let you have this without making you aware there was a charge. They are bound by rules to tell you and at the end, go over the sale with you so there is absolutely no mistake.
It would appear that you may have misunderstood what was being offered, but chances are they will review the call and make a decision based on that.
I also had the same problem. Recently spoke to retentions to request I move on to a deal I'd seen advertised on VM's home page but was told this was for new customer's only (because they're obviously more valuable than someone who's been with VM since the ntlworld days) and I couldn't possibly be given this deal. So I pared my package down, removed my V+ box, removed Sky Sports and was given a slight discount for 12 months. I also asked if I could have a new V6 box as my old TiVo was sluggish and hadn't been working properly for well over a year. I was told by the lady on the phone that even SHE hadn't had one of those yet and she was an employee so there was no way I could have one of those!!! I persisted though and she eventually decided I could have a V6 box. I was told there was a set up fee for this of £49.95 which I accepted. She then said, 'Oh! Wait a minute, no, you don't need an engineer to call as it's self set up'. I took this to mean I would not be charged the set up fee as I was doing all the work myself. So I agreed to proceed. AT NO POINT WERE ANY OTHER CHARGES DISCUSSED WITH ME. Three weeks later I receive my bill. My old bill used to be £111 a month give or take, but I was expecting my new bill to be around £64, minus a discount for overpaying the previous month. It was in fact closer to £170! On checking my bill I have been charged a £99.95 set up fee plus £14.99 activation charge!!! I DID NOT AGREE TO THIS! I assume VM record all calls because if they review this they will see I was not made aware of these charges and would not have agreed to them! Having had recent issues with the total lack of security on ntlworld email addresses (they consistently get spoofed or hacked despite constant password changes), I cannot face ANOTHER call to VM about their poor service so I'll be writing them a complaint letter and then going to the ombudsman. They just can't keep treating customers like this when we pay so much for their (frankly below par) services!
So today I decided to try reduce my bill cost and have my 2 boxes changed to the new v6 ones
Current package 200mb broadband, all channels plus Sports movies, asian channels, evening only free calls plus hd after all past promotions price has now reverted to £125 approx.
After seeing online that i could get the same package as a new customer for £85/month for first 12 months there after £120/m with Talk more anymore + £14.99 activation fee, and £100 Amazon, JL M&S voucher
I thought at trying my luck at getting a better deal
So for the same package being advertised for an existing customer (not clearly that this is for new customers only) was £96 (£11 more/month) plus installation fee of £64.95.
I did request them that happy to do a self install as all cabling is available so dont really need an engineer around to disconnect and connect a device, as there is not much more than a power cable, coax / cable connection, and hdmi to tv and maybe ethernet, all of which is straight forward to connect. but they said as i'm going for 2 devices they will need to send some one round to do this, if it was one then a self install would have been possible.
Eventually he reduced the install price to £14.99.
But still this is £11/month more for an existing customer, so over the year this is an extra £132 ohh and new customers get rewarded with an extra £100 voucher. So in total minusing any marketing cost for new customers, there is a difference of £232 for being a new customer. And i just did a seach via Quidco i would get rewarded a further £125 if i just clicked through them. so now the total is £357.
So what is the term loyalty for existing customers, how is this earnt?
I did ask what could define a new customer if i left, response was 3 months from leaving and returning. (question, is it worth the hassle of leaving and rejoining for a saving of £357, could you find alternative services for 3 month period) Is it best to switch between the providers Sky and Virgin. How loyal do you be to the providers given they dont seem to offer loyalty offers.
Once i get my new bill would be keen to see how the itemised bill shows up each of these line items and if its clear.