My read on the OP was that arrival at the airport was at T-75, 15 minutes before the check-in desk was supposed to have closed...and no one was there. If I've interpreted this correctly, I think that the OP has a very valid issue. I'd start by calling Customer Service and seeing what happens there.
Yeah, I may have misread that--apologies to OP if I did.
I'd agree that if they were there at T-75 and no one was at the ticket counter, that's an issue. I'm at a bit of a loss to understand, though, while all the TAs would be at the gate that far in advance of departure.