We guess the channel must have asked her to stay away from the grand finale of the show because of the false allegations she has put on the host of the show. The makers of the channel decided to cancel her performance at the last minute without giving her any justification as to why she has not been allowed to attend the grand finale.
Rumor mills doing the rounds now are that Pooja has decided to file a case against the production house. She also said that as per the rules and contract of the show, every contestant is allowed to attend the grand finale of the show and they can't violate the rules.
source:
https://news.tvbasti.com/tv/2535-pooja-bedi-lashes-out-at-%E2%80%98bigg-boss%E2%80%99-makers.html