找谁去要（Amounts paid by or in behalf of borrower)

我买房时的合同中有这么一条：
Amounts paid by or in behalf of borrower:
Adjustments for items unpaid by seller
County Taxes 01/01/08 to 6/16/2008 $4000

我现在收到税单$7000， 按理我应该只付$3000

我应该是找SELLER 还是我的MORTGAGE COMPANY去要这笔$4000