Did any of the persons who told it was not ready or back to their store yet give you a card with pickup date, or possible right information down in quick notes form while they were on the phone with the service dept.?
If they had, then you'd have additions to the original paperwork from when you took this computer to them. I would be calling the Better Business Bureau on this matter you are not getting answers and only a run around from this store. However you actually don't need any additionally information but sometimes it is helpful in filing a claim.
Myself, I would get the photocopies of all paperwork on this issue, and have it ready to send in the minute you call the Better Business Bureau, so that the person you speak to is who you can directly send it to.
What ever you do, don't back down from them just because they are a nationwide chain. You've invested in a product they are apparently failing to warranty in a timely fashion. They advertise about good communication, timely repairs, and service calls performed by their "Geek Squad".
Granted whether you or not you chose to file a claim is up to you, I don't want to sound like it is your only option.
Good luck.