Land rate dispute

Regards, to the respected lawyers I have a land registered in my mothers name as the sole owner,few years back we found a prospective buyer(Property developer) whom we agreed to sell the land at a particular rate for which he paid a small amount for an agreement to sale the land which was much lesser & not even 1/4th of total land cost as we were in dire requirements of money,but we accepted the money due to the situation, unfortunately certain unforeseen events developed due to which we had to postpone the sale of the land. But now we are in position to restart the sale process again & we requested the buyer that since certain time had elapsed,owing to time factor to re negotiate the land cost, but buyer has declined and has warned us to take legal action if we don't sell the property in same rate as was decided in Rs 10 stamp paper(Note the property registration has not been done in the buyers name). But we strongly believe the property prices have risen in that period & still selling at the same rate would be a huge loss for us, but now the buyer is intimidating us, I would like to know what Legal course will we have to take if the matter goes to court & are we at disadvantage since we have accepted a small paltry sum which is in equivalent to the land original cost,if required we are ready to refund the advance amount with interest,can the court still take an action against us?