Mortgages can be sold from one bank to another without your knowledge.  Different corporations are setup to "service" your mortgage - collect your payments, file lawsuits, foreclose, etc.
But the banks and the mortgage service corporations need to follow the rules -- they must be able to prove that they are owed money, that they actually have the right to sue or foreclose and that the amount they say you owe is correct.

If the bank or your servicer is not following the rules, give us a call.