If they installed a bogus XP to fix it and left you with a ticking timebomb, the issue is not something Microsoft may fix. You have to ask how you'll get out of this pickle.
The usual is to get your XP CD out and perform a PARALLEL INSTALL using your CD KEY to activate your license. Then you install all the drivers and then reach over into the old installation and save your files.
A while back, a year I guess, we had our dial up modem go bad and had to be be replaced. At the time we had Windows 98 on our computer, witch is a Gateway and 98 came already installed. Well Windows 98 would not reconise the new modem so the shop had to install XP to get it to work. No problems still get updates but we still get the message the our XP is not genuine. I have done sent Microsoft a e-mail explaining the problem. Any advice? I want to get this sorted out. Thanks