Very Unhappy

I purchased a tablet from Prosperoh in 10-2014, The tablet i received was faulty, I contacted Prosperoh and they advised that I need to take it to Mustek in CPT, which I did and received a credit not, bare in mind that the credit note was not the same value as what I paid for through Prosperoh, I sent the credit note to Prosperoh in order for them to send me a new tablet after all discussion and agreements, I haven't received the new tablet and it is 6 months now that I am paying for something that I don't have, Ever since January I have been emailing and calling Paul Van Zyl who is apparently the owner of the company and Elmie I don't know who she is at the company but nevertheless they are never avail to speak to, but up until today I have not received a call back from anyone of them and left messages with Claire, They don't reply to my emails and never return my calls, What do I do, Who do we complain to, I got an affidavit from the police but what do I do with it, There is no manager at the Prosperoh office you can complain to, Claire just says there is nothing she can do about it and she will leave a message they must call me back, Yet no calls returned, I am fed up with them,