Cannot install dstv

I can't complain about customer service, everyone who has helped me has been kind and tried to sort things out. However no solution. I live in a flat and trying to install Dstv. Signal strength tested, booster purchased. Decoder hd connected. It works for a while, then every day over the last 5 days I have had to call installers back. Sometimes when I change the channels an error message comes up saying faulty connection. Took the decoder to n1 city. They replaced it. When I got home with new decoder same problem. The whole process has cost me over R1000 in installation and not to mention hours of time over a whole week. Please help! Thanks