You'll need to call O2
Numbers here Guide: Coronavirus Community Help and Support
Advice from an O2 Guru regarding a way to get through:
If you call 202, when it comes to the reason you are calling stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to an advisor.
Press Upgrade, Lost/Stolen if you have to.
Veritas Numquam Perit
It's only a suggestion.
There's no need to respond or make any changes.
If you are out of contract, you can check your upgrade options in your MyO2 including sim only which may save you money.
O2 are trying to persuade customers off old tariffs on to the new ones.
Your tariff not being available anymore means it's an old legacy tariff which you would not be able to change back to if you moved to a new one.
Customer service has been impossible to reach since all this Covid situation kicked off. They haven't coped very well with it at all unfortunately.