Forged signature in building site plan

The promoters took our land for flat construction whose agreement was done 12 years back but till now no possessions provided. Now when we are preparing for legal proceedings it was found that promoters has done forged signature of the land owners in the building site plan which is also approved by municipality. It is having signature on a 2012 and 2014 site plans and the person died on 2010. Getting death threats from the promoter to shut the mouth and let them do the construction without any compensation provided.