Saxophones low notes?

I would most likely say that a key isn't closing properly. If you can hit the notes on another sax and before you dropped it, it's probably something is misaligned keeping something from closing all the way. Go back to where it was fixed, and tell them exactly which notes aren't sounding properly, and they'll have a better feel for exactly where the problem is and then they will be able to identify and repair it. If you mention you just had it fixed, but the issue wasn't completely resolved, they might even do it for free.