Look for another job elsewhere in another Grocery Store, whilst your working here... Supervisors get treated like crap regardless of the field your working in. Maybe you'd be happier doing the role you did before you became a supervisor.

Way I see it, you're doing a job with more responsibility, you should be paid more.

I reckon you stay here and look for other supervisor jobs, get an idea of the pay they get, how likely it is you can get it, come back with a negotiation.

I'm not happy with the pay I'm getting, here's why I'm good at this, been here for x amount of time, Ive been offered x pay by this other place, here's what will happen if you don't.

Gotta have the options to negotiate though in case they don't go with it. Make it win win, if I stay I get paid more,vif I leave I get paid more and people might not be dicks 🙏 get an offer first though so you have the option.

With supervisor experiance, you wont really be square one if youblook for another job... but id schedule a meeting with your superiors to discuss your grievances first.
Start with the fact that you took on extra duty and havent been compensated for that.
Then disciss the hostility from co workers if you really feel you need help but you need to come to the table with solutions too. Is there anything you can do to tackle the people issues first?

Don't mention the customers being rude. Thats the job and it tends to always be worse at Christmas time, ironically.. but you dont want to complain about something out of everyones control when trying to project that youre a good supervisor and should be paid as such.

I understand you on the last part...one of the reason I haven't left my current job too is because I don't feel like starting over again at another place.

Too many people are afraid to ask for a raise. The worst he can say is no, which shows you what he thinks of your value. Then you can look for work elsewhere and not feel bad about it!

Looks like you have the training and experience needed for another job now. It’s ridiculous not to give a raise along with a promotion. What a damned skinflint.