Contract expired but still being charged

I have joined virgin active fitness club, Bluff club in KZN for 12 months from last year February 2014. I relocated from KZN to Western Cape last year September 2014. My new job was too demanding and could not have time to attend the gym. So I allowed the contract to run out end of March 2015 but I was billed in April 2015 of which I had informed the bank to reverse the premium. Today, I received a call from an agent who claims that I must settle a bill of just under R2000 because my account was handed to them. Please resolve these claims because I obeyed my 12 months contract and not owe a cent from it.