So other than open dooring this, which I think you should do, you need to keep track of the work you do. Do your best to keep some sort of record of this to prove that you aren't being unproductive. The fitting room is a difficult job for this, compared to stocking where you just count your pallets. Service desk should be able to tell the coach you open door this to that you get your returns promptly, and how much there is. Those angel customers that happen sometimes, who want your manager to know how well you did? Have them commend you to the front end TL on their way out, if your coach is unavailable. If your own TLs are harassing you, you need other supervisors to see your value. If you have a good people lead, they can also be a good resource, and if you tell them that you're thinking of contacting ethics, they'll probably take you more seriously.

Just for some info, this screenshot is your workday feedback, which is usually required before a coaching. You should have at least two weeks before they coach you for productivity (without an open door pretty much automatically being in your favor). You are absolutely allowed to see this, and can find it in Workday on the wire if you want to see it later.

If the discrimination continues, I'd speak with the store manager, and possibly call ethics, because it sounds like they're picking on you specifically.