Am I able to appeal tax adjustment?

I live in the state of Wisconsin and filed for the Homestead Credit. My prior landlord would not return any of my calls and I had no way to obtain his signature on my rent certificate. Once I e-filed, it was requested that within 48 hours of receipt of my acknowledgment, that I mail the original rent certificates along with money order receipts. I was only able to find three of my receipts and sent them in. My refund was adjusted to only those three months verified, when I lived there for eight months. If I can contact him within 60 days, am I able to obtain an original, signed certificate from my landlord, submit it for appeal, and possibly obtain the deducted amount? Or am I pretty much screwed?