The rules governing investment property are different that that of residential property. You are somewhat limited if this is the case. You can try another short sale, hopefully at a higher price.
My experience is that you will have greater success of getting this resolved during foreclosure process. Keep track of all the documents that you receive. See an attorney asap regarding putting a plan together (i.e. litigation, bankruptcy, etc) You might be able to negotiate a consent foreclosure with the bank. Good Luck