I'd say call again, see if they will put it back on, Make some sob story or something. Who are you with ? I know with Verizon, it is tied to the number, not the hardware (according to a few reps I talked to), so if they can slap it back on if they really want to. According to the phone companies, they just make the cash off it, so they want people to do it...
As for fixing it, Not sure of any company, but, I do know if you want to try it yourself, dont just try to replace one, replace the combo (Digitzer and LCD) as the LCD WILL Break when you try to get them apart. I looked it up, it's not a quick or eazy process(you have to pull the entire phone apart to get to the screen, lots of small parts) so expect to spend $350+ on getting it fixed. I know just the LCD alone is like $250ish.
Your best bet.... If your going to spend $300+, just take your phone put it up on ebay, you'll get around $160-225 for it(broken like that) then watch ebay take your $300+ your winning amount, and buy a new phone, You can get a nice new or lightly used one for about $300-500. With some time and shopping, you can get around the lower price.
Just live with it or sell it off...I might even be interested if your trying to get RID of it...