Interest charged on 6 Month interest free account

Since RCS has taken over the Edgars accounts, the system is in a shambles. i keep on being charged interest month after month. I have called the call centre 4 times already and keep on being told it will be resolved from the following month. The RCS service is pathetic. you are ripping of public. My account 6 months interest free account. If i wanted to pay interest I would get a credit card. They tell you they cannot reverse the interest, This is not acceptable. i am now frustrated. Terrible service. Never had this issue before Edgars was taken over. Can a senior person at RCS please sort out my query once and for all otherwise I will close the account that has been running since Edgars started out. Totally disgusted with the service from RCS.