This is just one of the reasons caution should be used when doing short sales. It doesn't make any sense to most of us, but the banks just seem to take a long time. Your contract on the short sale addendum should have given the bank a specific time to approve after acceptance. If you are beyond that period, you do not have to extend and you can have them return your earnest money.
All anyone wants out of banks is an answer. You need to decide your breaking point. No one can make the bank give an answer. If your period has expired, the only thing you can do is indicate your hesitance to extend the contract. That MAY prompt action, but that is a very weak MAY.
There is regular time and there is "bank time". Bank time doesn't seem to operate on the same clock as the rest of us do.