Contract renewal

I've gone through the online renewal to be offered £27 a month for broadband only volted to M125, I was paying £24 a month up until this month.

I've called through to retentions as when you look on the website and all over comparison sites the price for M125 is £24. I do not understand how they can claim I have been "volted" to M125 as an offer when this is above the standard price. The customer service agent was no use and began to offer me £38 a month for the same package using her "personal discount". She had NO idea what the online renewal process was and kept on offering higher costs than the £27 I was already offered. I think she thought I was lying as she kept asking for an email with the offer - I explained I logged into my account and followed their own system but she could not see anything near that price on her end. 

She could not explain what part of my offer/contract then had been Volted if I've been offered more than the normal price for the same speed. Surely Volt doubles your speed so the offer would be M125 volted to the next level?

Now online it shows £28 a month for M125 volted speed and phone line. I have been a customer for 15 years and tired of going through this at contract renewal, seemingly paying more for being a loyal customer? If I leave VM and come back in 12 months I would be entitled to the new customer price. 

Is anyone getting any sense out of the retentions department? How can they offer a £10 a month increase on the same package as a "deal"!