payment was misapplied by creditor

I am in CA and have been dealing with a problem since January. The bank that carries my 2nd mortgage misapplied my January payment. The check cleared my account on 1/9/01. I have faxed and mailed copies of the check but they cannot read the number printed on the check that indicates the account that the payment was applied to. My bank archives my checks and the copies are generated from microfiche. The copied check is dark and reduced. My bank says that they cannot copy from the actual check. The bank that misapplied my January payment applied my February payment to January and March to February. They call every other day saying that I am behind on my loan. What can I do? Do I really bear the burden of proof to where the funds were applied? Any advice will be appreciated. Thank you.