Contract term/Account handed over

I had taken out a contract with Virgin Active for my son in Southgate Mall in November 2018 and due to him still studying it was difficult for him to access the gym during the week so he decided to transfer the contract to Virgin Active in Braamfontein. The contract was supposed to be a 12 months contract. I tried to contact the gym so that I can ask them to terminate the contact to no avail. I asked him to visit the gym and cancel the contract personal. He went and he never got any confirmation from them that it was cancelled. And now during lock down, I started to receive phone calls from debt collectors and to my surprise it was with regards to Virgin Active account and I was told I owe R800 odd. And at that time, the gym was closed and I could not do any inquiries. And during that period, the account seemed to accumulate or attract interest even though we explain that, due to lock down there is nothing we can do? Now the owing balance is R1025.42. My question is, how did the debt collect manage to reach me? Why Virgin Active did not try and contact me?