Live chat discount not honoured

Another 18 months - another real problem with my account.

My contract was up for renewal in May 2024, so did the usual dance and got a decent retentions deal - m250, mega tv, weekend chatter for £39, and BT sport for £9 p/m so £47 overall. So far, so good.

I then had a separate email offering a different but better offer for exactly the same but cheaper - effectively £21 for main stuff & £18 for BT sport, so £39 overall. Pre contract documents came through and I accepted this offer.

Then 10 days later I had the renewal contract through but instead they are now charging £116 per month. Absolutely not what I agreed.

I contact live chat to explain situation and after a while, they state that can't honour old contracts so need to go to £89 per month but the agent will apply a £40 discount each month, leaving me at a net £39. However this has not been applied, and my bill is now even bigger than ever at £137, applying £48 worth of 'contract changes'.

Can someone please have a look for me as I have no faith in live chat. Every time I renew something goes wrong through no fault of my own yet I have to spend hours trying to get these things rectified.