Becker Radio 1989 Mercedes 560 SL

I have a 1989 Mercedes 560SL and recently had a 12 CD disk player installed. Ever since the radio has been showing dashed lines across the face and it will not play. I took the car to a Mercedes shop and they reprogrammed the radio. It lasted for a day and a half then went back to the lines across the face of the radio. I seem to be in a catch 22, the Mercedes place says that the people who installed the CD player are at fault, and they say it is a Mercedes problem. Any ideas on how I can get it straightned out? Frank