Case on purchased property.

I had a plot of 4 katha of land which was under possession for last 2 year. in the said land 2 room house were there which was also under my possession. but from last 2 weeks somebody has locked my said room. on my inquiry it was traced that the seller of land kept the house on mortgage and for realization of money some one has locked my room. In this regard what shall i do to get back my room. though i had contacted local layer and send a notice to unlock the locked room from the seller. but exactly what shall i do.