Useless as usual

I took up an account last month it was advertised 6 months interest free, when i purchased the lady asked me if i wanted it over 6 months which i said yes. I was billed with an interest charge. after lodging several complaints i was called by a lady from your call centre who told me i would need to call another department to rectify this as she is in customer service and not accounts. I refused as this is an internal issue, why must i as the customer now call another department? i did the right thing when i took out the account, the manager was supposed to call me after 10am yesterday, he never returned my call. Pathetic service.