Not trying to pick a fight, but you have to remember that you paid $36 (U.S. conversion) for a
four-year-old
game. COD4 has been on the backburner for a while, especially when you consider that IW has released MW2 and is prepping for MW3's release.
I know that MP is a HUGE part of COD, but can you still play the campaign? If so, the game is functional.
I retired from the Marine Corps earlier this year and am working part-time at GameStop just to keep myself busy 10-12 hours a week and get out of the house. I always tell customers buying a game two years or older (namely COD4, WaW, certain HALOs, Gears, etc.) that they can't count on a reliable MP experience because:
1) The servers are old.
2) The community for those games have moved on to newer games.
3) Hackers have had plenty of time to ruin the games.
4) Game companies may either be out of money or working on newer projects so they've directed their attention elsewhere.
Sorry you're having issues, but I wouldn't count on help from IW for your problem. Cheers.