Bad service adn very rude staff

I resigned from Bestmed over a year ago, and just last week Received an email, addressed to someone else, instead of me, saying that I owed them app R3800, When I closed my account I was informed that all was up to date and that my final payment would be on the 2nd of October 2017, I was also informed that I would receive an amount (not specified) from my savings paid into my bank. Nothing happened. I recently called their debtors office and spoke to Reme he notified me that the reason for the long delay on the money I apparently owed was because they had changed systems. I then spoke to a very abrasive Tasha (Supervisor) , She promised to come back to me, Been 4 working days now , nothing. I informed their debtors department that I would pay of the amount on a monthly basis, as I am a pensioner and do not have a lot of money, I e-mailed them twice still no response, My Membership number is **********