Mobile number

1. As requested, I am writing to confirm that my mobile number XXXXXXXXXXX is currenly linked with my account at your bank.
2. As requested, I am writing to confirm that my regisetered mobile number is XXXXXXXXXXX, which is already being linked with my account at your bank.

Are both sentences grammatically correct? Which one is appropriate?

If you're trying to find out whether your mobile number is linked to your account you should use 1. The other version would be incorrect.

On the other hand, if the request was asking you to confirm your mobile number (the bank is unsure that their records are correct), then (2) is the better sentence, except for "being", which should not be there.