While the CRA investigates this account is not being included into your credit score. Once they are finished and if comes back verified then yes you would go back to the score you had prior to the dispute. You could contact the collection agency reporting this information and ask them to provide proof this is your debt and not your siblings.
Apparently the debt is in collection?
Requesting debt verification from the debt collector may not get resolution of the issue. In verifying a debt, they do not have to provide proof to support their finding, they need only obtain confirmation that you are considered the true debtor.
The heart of the matter is, who owes the debt? Does the twin fess up to the debt? If so, then a statement from the twin along with documentation of the name similarity would most likely resolve the issue, as they would have the admitted debtor to pursue. If not, they most likely wont give in until they have a party to pursue.
Their records, in their current opinion, point to you.