Suspension Noise problems of the 2015 Buick Encore

I had purchased a 2015 Buick Encore vehicle on March 03, 2020, that had a "not for sale" yellow sticker on the windshield. I had notice that the vehicle made a thumping sound under the hood on the driver side when riding on the highway. I took it to johnny londoff service dept. , but was told that nothing was wrong with it. In addition, to noticing that the vehicle would roll backwards on the smallest of incline. As time went on the vehicle would roll back, then roll forward on leveled grounds when I would take my foot off of the brake pedal. I took the vehicle back to johnny londoff service dept. , and again was told that nothing was wrong with the vehicle. I took it to telle tires and auto center and found that the suspension was worn out on the front and back of the vehicle, with struts and spark plugs needed. This vehicle rolls back when sitting at a traffic light, at, in line at a fast food drive through, and just everyday driving. Johnny londoff should have fixed the damages and/or repairs needed before selling me the vehicle. I would not recommend buying a vehicle or doing business with them.