I have had the same issue but have been treated appallingly.
I signed up to TNT via Stream for £5 a month for 18 months on the evening of 9 April. On the same evening I sent messages to friends and family telling them about the deal (by WhatsApp and iMessage). When I subsequently read an email from VM saying that I would be charged £16.20 I was really surprised. I Googled the issue and read on the VM forum that the right amount will be charged on the next bill. I also sent an email to VM Complaints raising the issue and asking for the £5 agreement to be honoured.
Two weeks after signing up for £5/month I just today looked at my bill and saw that I have already been charged over £25 for TNT - i.e. after just two weeks VM are charging me 5 times what I agreed to pay for one month of TNT.
I also heard back from VM Complaints by email saying that unless I had a screenshot of the £5 offer they could not investigate.
I then read other posts saying that even with a screenshot the £5 agreement is not being honoured with other customers. See picture below.
So, I called the telephone number in the VM Complaints email and spoke to a man who was at times, unfortunately, very combative, argumentative and kept on interrupting. He put me on hold for a long time as if hoping I would go away. He said that as I had no proof in writing in the form of a screenshot from my TV the £5 deal would not be honoured. I said I had contemporaneous messages in writing - in response to that he said that those messages could be made up. In effect the suggestion was that I am lying or falsifying documents. He also said that as I had received an email from VM Complaints I cannot get the £5 offer because of VM's "policies" regardless of what VM offered and what I accepted and regardless of how contracts (offer and acceptance) work - it is VM's "policy".
As well as VM not honouring a £5/month deal I know I signed up to, in the space of 2 weeks I have been charged £25 which is 5 times what I signed up to pay in a month. I did not agree to that. So I asked for that to be refunded.
The man on the telephone initially refused even to refund me the £25 I have been charged.
I asked him if he or VM had a screenshot of me agreeing to pay the amount I have been billed. He said no, but he said that as there was a subsequent email saying £16.20 that is what I had to pay per month. I pointed out that (1) I had contemporaneous messages (which he said could be made up) and subsequent emails to VM saying £5 but VM will not - without a screenshot - accept that contemporaneous or subsequent writing to prove the amount agreed, (2) paradoxically, VM is relying on a subsequent email - without a screenshot - to charge me £25, and (3) I simply did not agree to pay £16.20 or £25 in the space of two weeks - I agreed to £5 a month for 18 months - so there is no way I should have to pay the £25 I am being charged for TNT.
Ultimately after speaking to his manager he said the £25 can be refunded. I said that if they accept that I did not agree to pay £16.20 a month, they must accept that I agreed to £5 a month and that I want the £5 honoured. He said he won't do that. I asked who I can speak to for it to be honoured. He said nobody.
What is going on VM!?
As a customer experience this has been awful especially being told I would not be believed without a screenshot, that my written notes/ messages could be fabricated, and that I have to pay £16.20 a month or £25 after two weeks because a subsequence email from VM said so even though that is not what I agreed. I am in effect being treated as if I have fraudulently made up emails, yet VM can charge a sum I did not agree to pay.
How many customers are being over-charged for what they did not agree to, and not being given what they did agree to yet have not realised this yet? This seems like a con to me, yet I am the one being told I could have made up written messages and being told that I am not to be believed unless I took a photograph of my TV screen when I accepted VM's offer.
As soon as there is another provider on my street, I am going to leave VM as the customer service has been awful and stressful - in effect is suggesting that I am making things up and falsifying written documents. Nobody wants to pay somebody for their day to be ruined like that. And I would just like VM to honour what they offered me and I agreed to.
Here is the screenshot from another chat which shows what I saw, even though the other user says that VM will not honour the deal even with this screenshot:
