Can’t download any apps
I’ve put in my correct card details yet it won’t accept my payment method
What does 'won't accept' mean, if you got an error message what did it say ? And what are you trying it use as your payment method, credit card, debit card ?
If it's a debit card, and if you are getting a declined message, that might be why, not all seem to still be accepted by iTunes, and they might no longer be accepted at all in some countries.
For a card to have a chance of being accepted it needs to be registered to the same name and address (including format and spacing etc) that you have on your iTunes account, and have been issued by a bank in the country where you are (and therefore the country which is on your iTunes account).