Heater is blowing cold air?

I have a 2002 jeep liberty sport and I had it to the dealer 5 time within 6 weeks from getting it because of no heat. They changed everything and anything even flushing the system but still no heat. Now I have a massive oil leak and cant find where it came from ready to junk this jeep. Please help if you can. Thank you

They changed the thermastat, heatercore, blower and blower motor, flushed the system multiple times, and changed the radiator cap, even the controls they changed. I bought it in january 2012 for $6,300.00 so from that point on till now I did a oil change in september and they claim they did one when I bought it. I didnt have any oil leaks until 2 days ago and it leaked like 3/4 of the oil out of the engine and im afriad to start it again because I tryed starting it it sounded really rough idle and it misses now too.

I said to them about a possible head gasket leak and their mechanic replyed with if that happens there would be coolent mixed in with the oil and you would have white or a dark smoke coming outta the tailpipe. So now im without a vehicle because they messed up and didnt do the right testing I guess because they didnt say they did any of the testing what you mentioned. What would be my next step?By the way the oil is basically coming right back out on the ground.

I just had a mechanic come and look at it and it is the head gasket. Thank you for your time Roy