How should I deal with this

They’re bullying you. They want a reaction by the sounds of it. Hold your head up high, say hello, smile and walk on. They will soon tire of things once they see you’re not reacting. You’re are far better than them. Have you got other friends you can shop with? Take care and be strong x

Excellent advice from Mattsmum2! It isn't you who has done something wrong - it's the other women. Perhaps they wouldn't be so brave if they weren't together. Good luck!

My great-grandma would probably have stuck her tongue out at them.

Give it a try.

It doesn’t sound petty or insignificant, and I imagine how upsetting it must be. But some good advice given, make sure you don’t shy away from these women, if you see them just walk straight past them eyes straight ahead, even if you don’t feel confident try to give an air of confidence.
Don’t let them cause even more trouble by staying indoors. If they think they have succeeded in bullying you into staying away they could do this to someone else. And as has been said, like all bullies they will lose interest once you are not reacting the way they want you to react.
All the best and remember you can do this, you really can 💐💐