Depop help please

[bendmeoverbackwards]

Dd wanted to buy a jumper on Depop but her card was declined for some reason. So she then tried to buy the same jumper from a different seller, card was also declined.

Then after some time she found BOTH payments had gone through and now she has been charged for both. Both sellers say no returns. Anything she can do?

Are they uk sellers?
If bought online you have the right to return items

Although if they are private sellers then the law is not so clear