Owing money for freezing membership

Hello I have a problem with virgin active. 2019 I had membership with virgin active and the same year COVID19 happened so I had to freeze my account since then I have never been to club so surprisingly last week I received a call from the club telling me that I owe them R600 for what because I have full 2years without setting my foot on the club now they want money. The worst part is that they have nerve to call and tell me I owe them but when they unfreezing my account they didn't tell call me telling me that they have unfreeze my account please assist me with this matter