read the meter still doesn't tell me if they owe me money or not

where do you go to do this and how will I know if sp have made alterations

unfortunately we have always been with sp as no other company will touch comfort plus heating but they wont tell me why

2 years ago I owed Scottish power £900 they put me onto a prepayment meter, 1 year later I only owed them £100 this year I thought when I received my bill considering nothing has changed except that prices have gone up a bit that they would owe me and then they would change the settings on my meter I waited and waited for my bill but it never arrived so I called them up and after a heated debate with the call centres manager he told me that we were all square and that the explanation would be sent out with the bill, surprise surprise no bill and no explanation am I just being paranoid or do I smell a conspiracy could someone enlighten me do I deserve a rebate or is he right considering that he admitted that no alteration had been made to the meter but I don't understand how it works .please help me