Bad account department

After we bought close on the account in my husbands name, we made payments on the 10th of each month, as we only get paid on the 10th of the month. Every month they are calling us before the 10th to ask about the payment due. Every month I explained to them we are only getting paid on the 10th, they then confirmed with me that it is fine and they will make a note on their system that payments will be made on or after the 10th. But it seems to us that the note on their system is not made or it disappear from their system. I paid the account in full in January 2020, and now we still receive notices from them that the account is in arrears. According to us there are no outstanding fees. The reference to them is that they are showing on the account,the same as in the past. I really think that the staff in the account department need urgent training in how to handle EFT payments and reading bank-statements. If they send us a letter or any notice again I will surely take legal action against them as they give us bad name, I also expect a written apology from them as they are ***********. I will also make sure that nobody we know will ever buy from Mr Price again.