It might be a scam honestly, i would say open a dispute with them. Mercari is a lot better btw, way cheaper. Mercari also holds the money until your item is delivered and you inspect and review the item.

I'm a bit weary buying from depop, last time I bought from them. It must have taken a month for my parcel to arrive.
The company depop is a legitimate online business and they do take your money right away if you pay by debit card or credit card
I recommend buying from ebay it is alot faster and they provide you with a tracking number

This is a very common scam in Depop. Sorry, you can't just buy from any website, you have to research platform reviews to tell if you are risking your money.