Galaxy Tab & Retail Mode

So I made the mistake of purchasing a Galaxy Tab A (SM-T550) from someone on craigslist. It turns out it's locked in Retail Mode. I've tried all the 5444 passwords and such to unlock it with no luck. I downloaded Odin and flashed it with the appropriate firmware...and no factory reset doesn't work (it's locked by the MDM)....What can I do? Is there any possible way to remove the retail mode? Please help, I'm somewhat technical so I'll try anything.