Bad Service

I gave my computer in to get fixed on 15 December Within the hour they phoned and told me what was wrong then a few hours later they phone again telling me that it was fixed and that it would cost me R1000 I told them that ill get the money together and then ill come and collect it. Today 28 December we phoned to let them know that ill only be able to collect it in january they told me that they don't know about the computer. My wife went down to them to tell them in face to face because of this miss comunication. She told the and the person that she told went to the back and came back with a computer and asked is this your computer and it was not our computer then he came back for a second time with the correct one showed her what they added on the inside and pluged it in and it did not work she then told them to remove the RAM they added in and put back the one that was in there before and give back the computer they then did that and told her that the covers of the computer are missing and then tells her buy a new computer for R3500.... How does this work the biggest computer company lies to a customer and also losses there property after trusting them to work and fix a problem