Easy Anti-Cheat Doesn't Work

Posting again because I haven’t found any fixes and I’m 5 days away as of posting this before I have to refund, but I’d prefer not to.
I have the Halo: MCC but anytime I try to get into matchmaking I get a must enable easy anti-cheat (EAC) error. I start the game with it enabled but by the time I’m in the menu it’s already off. I’ve tried everything I can think of; verifying game files, repairing EAC, re-downloading the game, reinstalling Steam, downloading newest C++, giving admin privileges, allowing everything through my firewall, downright turning off my antivirus and firewall, but nothing will work. I only have a couple days before I can still refund so any help with this is appreciated

> 2535429134695990;1:
> Posting again

You already have a thread.