Homechoice charge interest on zero outstanding

I bought an item from Homechoice 2 years ago. Yes due to financial reasons I fell behind on my payments. In July 2018 the person from Homechoice phoned me and I made arrangements to pay te full outstanding amount in July 2018. Now 19 February 2019 they keep phoning me with an outstanding amount for interest on a zero balance, because I never closed my account. Now the first problem I have is that for all the years buying from Homechoice I never had to close my account after payment was fulfilled. Second is that the call centre or collection person never informed me that after the account is settled, I must contact them to close my account. It is anyway the first time in my life that I hear you must close your account... But I can say for sure that I will never buy from them again...