General Motors

I received a letter dated may 8, saying that my car may be experiencing these problems. Bit when I contacted gm they said that the service repair had already expired. Bit to contact local dealer and the liaison would work with me. Spoke to liaison, she told me to drop off car and they would diagnose problem. If it was diagnosed as a gm problem that gm would be responsible to cover cost. Car has been at dealership over a week. Got a call today, say that it will cost $2k to fix car. I asked what was the diagnosis, she said we don't know what's wrong with it. I asked well how do you know how much it will cost to fix it? She said we can change the oil, then you can drive for 1k miles and then we can dx it, and if that is gm problem, gm will only pay 10% of the cost to fix it. I have the service bulletin dated jan 2020 that describes the problem I am having and how to dx and how to fix it, and there is no expiration date on it. I want my car fixed at gm expense, because it is a gm problem. What is going on with gm? Help