Hi I’m having a problem adding my card
Need help it keeps saying decline payment and I haven’t purchased anything
A declined message doesn't mean that you have bought something, it just means that the card is declined.
If the card is a debit card that might be why it's being declined, not all seem to still be accepted by iTunes, and they might no longer be accepted at all in some countries. Do you have another card that you could try (preferably a credit card) ?
Changing / removing payment details : Change or remove your Apple ID payment information in the iTunes Store - Apple Support
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)