Capitec blocked my account

I buy and sell second hand phones on Facebook and Gumtree. I recently advertised a phone and sold it to a man who agreed that he read my advert carefully and upon meeting and viewing the phone, he checked everything and agreed the phone was to his satisfaction. He did an eft payment into my Capitec account. The next day he contacts me complaining about the phone as he bought it to resell and couldn't do so. He purchased the phone from me as is and agreed to its condition etc. He demanded a refund and I declined to do so because I had ensured that he checked the phone properly. He then proceeded to contact capitec and stated that I am a ******* and they blocked my account. After contacting them, they said I should get an affidavit from the police station stating what transpired. I did so but when I went to capitec to resolve the issue, no one was willing to help me, they were rude and arrogant and told me I must get the man whom I sold the phone to, to give me an affidavit stating I am not a *******. This man is clearly being petty and is doing all this just to spite me, blocked me and I can't contact him so how is it possible for me to get an affidavit from him? If I was really a *******, I would not have went to the police station and written out an affidavit of the event. I would have counted it as a loss and moved on. Capitec refuses to help me. They seem to be siding with the man.