Respected sir/ madam!
Since you have paid the advance payment towards work and GST was paid by you and the service wasn't provided, meaning thereby they would not have paid the GST amount with the GST office. You are entitled to recover the whole amount including the GST amount paid by you from the trust. It all starts by sending a Legal Notice first. An expert advocate can draft a Legal Notice that would start the legal process, if your amount isn't still refunded, with the help of your counsel, you can file a commercial suit against the trust under Commercial Courts Act and get your amount refunded back in the most speedy way possible.