No payment of Items purchased

I had sold some items to Nikita Lehman and a collegue over 4 months ago at which stage they asked to pay off the items over 3 months to which I agreed. However now after 4 months I have not received a single cent for goods to the value of R1,350 and they have already used the items so no use in even returning it to me. I have made contact with Nikita on numerous occassions to which I receive absolutely no response.