Credit Provider giving false information

So I have a default on my account that I paid off as soon as I learnt about it. Without getting into too many details it was a combination of misplaced trust and ignorant mistakes that lead to it. I was never notified of the debt and when trying to get it removed from my report after paying it the credit provider told Equifax that they had notified me, at the address I’m currently living at, on a date before I ever moved to this state. They gave false information to Equifax. Has anyone had this happen to them? I’m trying to contact Equifax to find a next step but anyone who’s been through a similar thing and would be able to help would be greatly appreciated.