Tymebank robbing me

2 weeks ago I was selling my Mobicel phone for R300 on Facebook. A guy contacted me saying he wants it. He came and told me he doesn't have cash he can transfer money to my account. I agreed. The guy transferred R300 into my Tymebank account and I managed to buy R20 airtime to check if it's legitimate. The following day Tymebank blocked my account. I tried many many times calling them while they transferred me to ***** department and no one assisting me. I wrote emails and still they don't explain why my account is blocked. This bank is taking advantage of people because they don't have branch. Masepa fela marete abona msunukanyoko. I want my money.