Wrong mortgage paid off!

[San Prasad]

We just sold an investment property, but my husband inadvertently gave the settlement company the account number for our primary residence mortgage for the payoff (though for anyone checking, this account was clearly associated with our property at a diff address in a diff city but the mortgage amounts were similar) instead of the account number for investment property mortgage. 

The sale closed, keys & title changed hands, funds were disbursed - but when we called the mortgage company a week later to discuss escrow refunds, we discovered that the investment property mortgage was, in fact, intact and that our primary residence mortgage had been paid off!

We made a clerical mistake, but no one caught it at any stage of the process! Our primary mortagage has been paid off in full (different bank from the investment property bank) and recorded.

What is our best recourse here? We really don't want the sale to fall through to get reversed (is that even possible after closing). And it is incredible to me that something like this could happen with no one catching the error! Any ideas on how to proceed? Should I be posting this on some legal site? Thank you!