I rang up last week and just told them straight that i would like to be treated the same as a new customer as if i moved next door I would get a better deal. If not I will give you my notice and leave as there is no loyalty. This was with the cancellation department (customer retention0, Fair play they gave me the deal and it is 18 months and I said that is great as it falls inline with finishing just before xmas 2024 and even better deals then. As you can get the black friday deals that is what the lady told me. I was polite with them.
Good luck and do not be afraid to pull away either I mentioned money is tight and they did acknowledge this so I expect they are also knowing they need to keep customers.