cant update my payment method mobile billing

i created a new icloud account so i updated the payment method and chose mobile billing.

i filled in everything and also my phone number which then needs to be verified.

they sent me a code to verify my phone number and i received it anddddd typed in correctly so i proceed to verify but then theres 'an unknown error has occured. Your request could not be completed because of an error. Try again later.'

ive tried this multiple times already and its still the same. What should i do/