Extra payment

[Cmg1]

I paid off my device plan last week and upgraded to a sim only plan. I have now been charged a payment despite paying off the plan last week. 

[pgn]

If you upgraded, your first bill will be a bit higher than usual as the old and new tariffs balance out.

Nobody here can see into your account, you need to contact O2 if your MyO2 is not allowing you to see what is happening, @Cmg1 - https://accounts.o2.co.uk/signin

Ways to contact O2 all in here: Guide: How to find help & contact O2 - good luck!