I've had this machine 20+ years. About 6 yrs ago I decided a new one was in order. It works great as well. Most issues are solved by cleaning, new needle and rethreading. I don't worry about top & bottom thread matching, in fact I've used 30 wt on top and 6 wt on bottom with no problem.
With that said, your problems are not "in your head" nor is it your fault. They can be fixed (the store may need further training) or the machine can be replaced if the store refusses to fix them. Also, call the manufacturer, they don't want to loose unhappy customers