Unfairly blocked

Goodday my name is Solomon Mpati ,in May this year I resigned from cash converters Benoni as a buyer,a month later I went back to the same store to cash advance my sound system and I was helped with no problem.the following week I went back to cash advance a different item,this is the time when I was denied service by the owner of the store and He never even bothered to tell me why,I left the store without making any noise.yesterday I went to carnival mall to sell my laptop,agreed on the price with the buyer and as he was about process the buy he noticed that I’m blocked on the system,I can’t sell anything .i need An explanation of why am I blocked please