Engine/transmission 6.6has

[Jp3313]

I recently had an oil change completed on my vehicle then took my trailer in tow across the Atlantic provinces with my family. Approximately 1200km after my oil change I received the “oil level low” notification in my dash.
I pulled the dip stick and there wasn’t an ounce of oil to be seen.
I poured 6 quarts of 5w30 dexos in and was able to see the oil level again.
After checking my oil constantly I noticed she was going down a bit while towing, so I kept topping it up.
Once my vacation was nearing end, at approximately 100km from my home, my truck had burst a transmission line and spilt oil everywhere.
She’s been in the Garage now at a GMC dealer for 3 weeks, and I still haven’t received a proper answer or time frame of when my truck will be fixed or even what is the matter.
And this transmission issues doesn’t explain the oil burning. 

What should I do?
Is this normal at only 44,000km?
Does the 2500HD 6.6gas really burn a full base of oil and then some after towing for less than 1200km?

Need help.
Still making payments on this vehicle and it’s at the garage with no loaner available, what are my options?

It is under warranty for 2 more years.