Purchse of residential plot from sc

Sir I purchased a residential plot last year, registry and dakhil is also done but now SDM declare that plot is govt land giving reason that permission was not taken before purchase from DM as the seller belongs to SC community. Sir I invest all which I had .I want to know that how registry can be done by registrar and even in mutation paper Nayab Tehsildar sign that seller does not belongs to SC/SC then how would I know.plz Sir help me that is residential plot and not agriculture. And seller has no objection. But why Govt grabbing my plot as they are the only authority from which I got registry done