HOMES BY AVI fraud in the condition extention agreement Internet

Reps in Avi showhome in Walden Calgary (Homes by AVI) signed a conditional purchase contract . The condition in the purchase contract would expire by April 8,2013. On April 7,when I and my wife went to their showhome in Walden a, the saleswomen Ashley asked me to sign a agreement to extend the condition date to April 12 and we did have a copy of the . My wife an i signed the agreement. But in April 9 evening they informed me the purchase contract was cancelled. I went to their office. And their Reps said they ony signed at the witness and they were not on behalf of Homes by AVI. Because the agreement was not signed by Homes by AVI, so that's why the agreement is void.
I have been aware that the lot hold agreement and the purchase agreement also were only signed by their showhome sales person.
As Homes by AVI doesn't honour the condition date agreement, and their sales person mis led me on this this matter which led to my loss of the lot.
I seek your help to solve the problem. My objectives are to let Homes by AVI honour the condition agreement and continue to execute the purchase agreement