Cell C WIFI

I received the call from Nimble group saying Cell C handed me to them because I owe them I didn’t receive any notification or claim from Cell C that owe them , I was using their WIFI then I stopped using it I didn’t know that I’m owing , now I’m told that I have to pay the interest for missing that payment to Nimble , i can’t pay the interest if I was not told I’m owing, my account number is ***