mbd debt collectors

I was called and told that my Virgin Active gym membership is in arrears, however this membership was cancelled a while ago. The consultants told me that it was not actually cancelled and that I have to pay R1800. I agreed to paying this in 2 installments, R1000 first and then R800. They debited the R1000 in Feb, and they debited another R1000 in March instead of the R800, they've taken more than they should have. I'm extremely appalled.