I had this issue about a year ago, I don't bank with Santander but Amazon were asking for exactly the same thing, basically they wanted a letter from my bank, Amazons requirements were that it had to be on headed paper, wet ink signed and stamped showing my address and account number.

We all know that banks in the UK don't offer this letter that Amazon have been requesting but I got SUPER LUCKY...

I went to my Bank and spoke to a member of staff that was extremely understanding and helpful, it took a couple of visits to the Bank but after showing her the email with Amazons demands she went ahead and created the letter for me with EXACTLY the information Amazon were asking for, I was extremely grateful and sent her some flowers.

I uploaded the letter to Amazon and a week later it was all resolved.

So, from my experience, you need to go to your bank, explain the situation and hope you get a friendly member of staff that is prepared to help you, be nice it's not the banks fault that Amazon are asking for something that isn't available.

Unfortunately, if you are outside the UK you may as well give up because you won't get the letter Amazon are asking for, as others have said, it is NOT a service that you can get from any UK Bank

They are NOT asking for a certified statement (I know because I tried that first, even got it wet signed and stamped on headed paper at the Bank), they are asking for something really obscure that is virtually impossible to get from a UK Bank without visiting a branch and actually speaking to someone that may help.

I hope this helps