MTN needs to be professional

I received a call last month with an offer to purchase a laptop. I accepted it the terms and got the laptop delivered to me. When it arrived the laptop was not what me and the person who called talked about. I sent emails to enquire about the return of the device no response and then I went to the store and I was told to get an affidavit and proof of address. I got them and returned the laptop. Now I receive a statement saying I should pay for the device I never even used. I emailed them and they rep**** to say I should give details and I did that. I'm supposed to make a payment but now I don't know which amount to pay. Because if I pay the normal amount they will close my account and I won't be able to use my phone and receive calls. Until today they haven't help led me after almost 4 emails and calls.