car registration and warrent problems

I bought a car in December and I was told that I would get a new vehicle registration in January because the DMV is closed, now in April still haven't gotten the vehicle registration and the current one expires next month. I called them they told me to do a Dekra report which they paid for it but the car didn't pass the inspection because of an oil leak when I notified them "We buy cars" I was told they won't fix it because I had been using the car for three months so is my fault the car has a leak.

when I try to claim via warranty that I got when I bought the car I was told my warranty is inactive because we buy cars did not pay which was surprising because when I purchased the car, I also bought a 2 years warranty

I've been following up with them for more than two weeks to 3 weeks and still no help.