Incompetence when canceling membership

I canceled my membership October 2014. They still had debit order rights and as far as I the leftover money in my savings was paid out so i thought this was a chapter closed. in 2013 I changed my email adress as well from @yahoo to @gmail, even my cancellation letter and all other correspondence over the last 2 years was done via the new address. <br> <br> 21July2015 I get a call from CreditWorx, the debt collector company that they use informing me that the case has been handed over to them and I owe them R543.64, I was shocked and angry as I had not been contacted by Bonitas personally, apparently they sent me a invoice (on the old email address that is no longer used), they never once phoned me. <br> <br> I immediately paid the money owed that was owed to them. This after having to phone 5 different people and numbers to get to the source of the problem. <br> <br> This was handled in a totally unacceptable manner, had they just confirmed receipt of the invoice (by phone) or even posted the invoice, or even better taken the money as they had debit order rights on my account, this would have been settled months ago. <br> Best off all, I received a membership invoice today 8August2015 indicating they owe me