Seller refusing to give prorated rent and tenant security deposit

[Beenna Han]

So I purchased a multi family unit that has an existing tenant in Maryland. I closed the purchase deal on late May, and soon after the closing I realized that the settlement did not include prorated rent (around $300) and tenant security deposit ($1200) related to the existing tenant. 

Unfortunately my real estate agent and title company did not check that these items should be included at the closing and I, as a first-time home buyer, did not know either at that time. So after the closing, I asked my real estate agent to contact the seller and asked for the prorated rent and tenant security deposit. The seller refused, saying the seller already used up the security deposit because the tenant did not pay utilities thus no security deposit left, and they had some financial loss because closing was delayed because of my mortgage lender's issue thus no prorated rent for me. After this refusal the seller never responded. What should I do? Are the real estate agent or title company responsible for this because they missed to check these items at the closing? or Can I do some small claim for asking these items?