You should have asked the rep on the 800# to ring MSP for you. Maybe they would have answered if they thought it was one of the big boys.
I had a similar experience with Budget a couple months ago at TLH. They're off the property and the house phone alternated between busy and unanswered. I finally asked an Avis rep and he told me they closed at 9:00. My TA had reserved a car at an agency that closed before my arrival!