Both the Courts below upon appreciation of the evidence, both oral and documentary, adduced by the parties, have concurrently found that if really the appellants-defendants did not execute Ex. A1agreement of sale dated 10.11.1999, they ought to have responded to the legal notice, which the respondent-plaintiff got issued to them prior to the filing of the suit, calling upon them to execute regular sale deed. The appellants-defendants, instead of giving reply to the legal notice got issued by the respondent-plaintiff, kept quite. The appellantsdefendants having not responded to the legal notice got issued by the respondent-plaintiff, the Courts below held that they are estopped from challenging the contents of the legal notice, which the respondentplaintiff got issued prior to the filing of the suit.