Worst account ever!!

I got retrenched due to lock down and my account was handed over eventually I paid my account up to date and when I asked if it could be closed they said i must wait a week before anything could be done as per the accounts department the very next day they called and said because I was handed over I need to pay am extra R500 why wasn't I told about this the day the shop assistant called in now I'm getting messages and phone calls to say I must pay that or the account won't be closed ?!