Outstanding amount on a paid up account with a paid up letter

We have paid up our Edgars account in 12/2021 and received a paid up letter on 23/12/2021. Now all of a sudden consumer friend is saying there is an amount outstanding of over R1800 which we don't know where this amount is coming from if the account is paid up . This is unacceptable !! How can we owe on an account which has been paid up last year already ??!!! My husband has sent through numerous mails for this to be sorted out as we are not liable for this amount which all of a sudden just came out of no where . Our debt company has also sent through mails to follow up on this but she also has not received any feedback either . When we call we are not getting proper answers just that we should pay this amount .