Not so happy ever active as they say

I the account holder went to close my account with virgin active Green Acers (PE) end of January. Reason ... because contract ended. Spoke to the guy at the desk .He told me he will close it for me as I payed my last amount . He did something on the computer and told me my account is close now I don't have to pay anymore. So I asked him don't I need to sign anything to show I'm ending my contract. He rep**** NO Sir you don't need to. I believed him and walked away with only the slip from the last and final amount I payed. Two months later I get messages from virgin active that I owe them money. I went to query but they don't want to listen to me and accuse me of lying. I also showed them my last slip when I did my payment. Long story short .... They handed me over to the lawyers and now I must pay an amount of R2400 because their staff was not trained properly. I did research and I found out I'm not the first victim. Bad service from virgin active Green Acers.