got all auto parts sold me a faulty transmission still under warranty they will not respond to my calls or work with me on fixing the issue truck sits in my driveway broke bay city Michigan

I purchased a rebuilt transmission (4l60e) for 550.00 dollars with a two year warranty. Transmission is still under warrenty. When i got the transmission i had some issues with the wiring in the value body area inside the transmission pan. They replaced that and it seemed to of solved problem. Now iam having a big issue with the transmission kicking out of overdrive and into drive, Which then the speed odometer decresses in speed till u let off the gas pedal then it climbs back to its normal speed and kicks back into overdrive, till u hold it steady again then it repeats the same thing over and over again. It starts doing this right after the transmission warms up. It took me 6 weeks for the frist issue to get resloved. I have tried calling them several times to get this issue resolved and they will not return my calls, I have also left several messages with no response. The truck sits in my driveway and has cost me a great deal of trouble getting around. I'am scared to drive it , I dont want anything to happen that might cause me or other drivers issues on the road. I'am on disabilty and feel i have been taken adavantage of. I dont have much money to fix it again , so it just sits here as i am still tring to get this resolved. I'am exausted with this issue can Someone please help me, i feel i have been ripped off. I have my warranty in hand i purchased it on 3/29/2013 invoice #1875 and it expries on 3/29/15. this issue needs to be resolved.