If the IRS had the correct information for the second stimulus check, the only way that they would use a different account than that one for the 3rd stimulus payment is if you instructed them to deposit into a different account. If you filed your 2020 tax return already, for example, and accidentally used the old/closed account and the IRS has already processed your return, then they might have gone by that incorrect information. But, again, unless you told them otherwise, they would use the same account as the second one.
