Crest Cadillac

I purchased a Certified Preowned 2015 Cadillac Escalade from Crest Cadillac in late 2016. I began having mechanical problems almost immediately and was initially told repairs couldn't be made because "it had been in an accident". The dealer quickly rescinded (due to the clean CarFax I was given at purchase). I later found out (from another dealer) that the engine had been replaced prior to my purchase. I was never told about the engine replacement. The dealer offered to buy the vehicle back several months after my purchase for $12,000.00 less than I paid for it. I was so offended that I didn't accept the offer. Now I realize that I should have taken the offer. After 70+ days in the shop over a 16 month period, I complained to Cadillac about the issues. Today I was told by the Cadillac adviser that the dealer is banning me from getting service. I'm not sure what I did to deserve this as I've always been kind and respectful to the service department staff. Please be careful before you purchase a used vehicle from this dealership as I would never wish this nightmare on anyone.