Car Trouble At Repair Shop

Car was running fine (2019 Mercedes benz a220 80k mile)… I went for an oil change at a oil change shop. Guy asking me what plug goes to what, and idk..and he stopped asking questions. They finished my oil change and soon as I left the lot my car started bugging out Transmission issues. Like skipping 2 and 4 gear, it won’t go pass 5th gear (7 total), it wouldn’t go in reverse, and the trans went out mid drive. I take it back to them and they say it’s not their fault And I tell them “my car was running perfect, I come to yall for a oil change and your worker asking me shit and now my car is fucked.” And they swear and say it’s not their fault and I been had these issues and my car just never showed symptoms or light come on. What can I do? I just can’t believe a perfectly running car just fucks over immediately after a timely oil change. I was only 120 miles past oil change. I’ve went way longer upwards to 600miles no oil change in my last benz. Only don’t have it due to hitting deer.