Will not zigzag

Question

I had my Singer 2808 sewing machine serviced some time ago. I didn't use it for a long time after that but yesterday when I tried to zigzag I realized that it won't zigzag anymore. It is forming a straight uneven stitch for every zigzag stitch I select. Actually, the needle is moving from side to side correctly but it is not picking up the thread from below. Now even the service guy refuses to accept it as his fault as a long time has passed. Would really appreciate some advice...