Angry former client

in 2013 I cancelled my vitality as I no longer worked for Discovery helath and that resulted in my Virgin Active membership being suspended . My access at the centurion gym was being denied as Vitality was no longer paying half of my gym fees and my account was no longer being debited . A couple of months later I get a call from debt collection company that I owe Virgin Active money, I then wrote a review on hello Peter and got somebody in finance to call me back. After a lot of dispute and back and forth emails and conversation I was advised the debt would be cancelled as I was billed in error. Four years later I get a call from again from a debt collection company saying I owe virgin active money. What i also don't understand is that after four years the debt re-surfaces , what was missed four years ago that all of a sudden you guys get and miraculously discover that you missed this debt .