Thanks for your post on our Community Forums, and a very warm welcome to you!
Sorry to hear there's been a duplicate payment made on your account.
You would be best placed speaking to your bank in relation to the payment, as they would be able to complete an indemnity claim for you, for the payment made, or you can leave this credit onto your account, to cover the next bill that's produced on your account.
If you go down the indemnity claim route, I'd advise requesting the manual payment to be returned to you - this will ensure that no credit file agency can then mark this down as a missed direct debit.
An indemnity claim would ensure the funds are returned to your account is a much shorter time frame than we'd be able to offer you.