Section 205.11(b)(2) states that a bank may require the consumer to give written confirmation of an error within 10 business days of an oral notice. If we require this to provisionally credit an account, can we refuse to provisionally credit the account if the written confirmation is not signed? Is the customer "confirming" anything if they do not signed it?

Technically, no - it's just a piece of paper. On the other hand, what if you are notified via email with no signature? There really is no down side of not having the signature as it's not required by the regulation, it's an internal policy and up to you.

So... "No" we cannot deny provisional credit, or "No" they are not really confirming anything?

If I was reviewing the file I'd ask if you contacted them and advised them that it would have to be signed. I would also look for any form you had the customer complete that was signed already, such as the commonly used affidavit or other claim document.

In part it comes down to whether you believe the claim to be valid or if you are trying to delay paying the consumer for some other reason. While that is not part of the investigation timeline, it would indicate whether or not a greater sample would be requested in a review.