It's a bit odd that taxes would have been withheld on an escheatment. Did you receive a Form 1099-R? If so, the withholding should be present on line 4. If you did not receive a Form 1099-R, try contacting the bank to obtain one. The bank is required to issue a Form 1099-R if there has been any tax withholding. However, if this Form 1099-R is for 2015 or earlier you might be beyond the statute of limitations for being able to claim a refund.
If the bank knew your SSN to be able to take withholding, it seems odd that they couldn't locate you, but I suppose it possible. If they did not know your SSN, I don't see how they could have withheld taxes and paid them to the Treasure for your credit. If they did not credit them to you you should try to recover the money from the bank.
You can obtain your Wage & Income transcripts from the IRS to find out if the bank filed any Form 1099-R crediting you with this withholding: https://www.irs.gov/individuals/get-transcript