Hi @Anonymous I doubt you will ever get O2 to offer cheaper deals to existing customers. You have to look for these yourself. (I upgraded at the beginning of the month when they had a sale and I am paying less this year than last for the same tariff)
In answer to the last part of your post about leaving O2... follow the advice here
Getting your PAC to go to another provider https://community.o2.co.uk/t5/Pay-Monthly-Pay-and-Go/How-to-get-your-PAC-2017-Update/ba-p/1052278 (this includes info about keeping your number )
@Anonymous O2 have operated on a 'fair deal for all' policy for some time now. Loyalty hasn't counted for anything for years. O2 also have a policy regarding Pay & Go sims that you have to carry out a chargeable activity once every six months or the sim will be deactivated. It's in the Terms & Conditions. It's not O2's fault that you put credit on a sim and didn't use it.
I'm not sure what it is you think you should be getting, or why you're complaining? Whatever you do or don't do with your phone is your responsibility. O2, and every other network are there to provide a service. You can change how you are contacted, and how often in your MyO2 account.
The others have given you links as to what to do if you want to leave. First thing you should do is make sure your coverage will be adequate from another network before you do anything.
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