Unsatisfied with Edgars

I have an account with Edgars for many years and my account always went directly to my son's PA. On the 14th of June 2018 she was sick and the account came to me. I knew I never owed them any money and I started checking the account and they realized they are charging for a cellphone insurence account since 2016. I didn't even know that Edgars had a cellphone department. I've never sighned any agreement regarding this and I've never got any proof regarding this!!!!. I went personally to Edgars in Sandton City to the cellphone department and customer care and have phoned Edcon complaints to try get to resolve this problem. Spoke to a number of people and said they will sort it out. Sibusiso, Lerato, Ngwato, Phumla. Reference numbers: ********** 0524GO, EDCP180 ********** 296, ********** 671053, ********** 684019, ********** 0770GO, EDCP180 ********** 929. Now they starting to charge me interest because I'm refusing to pay this. I am absolutely desperate to stop getting threatening letters from Edgars.