Interior designer cheated on me

I have been enduring a difficult experience with my interior designer for several months now. We have already paid the full amount, but the individual has deceived us by providing inaccurate square footage and subpar woodwork quality. Furthermore, our flat has not been handed over to us since December 2022, despite their promise. It has been nearly a year, and as ordinary individuals, the burden of paying both rent and home EMI has become overwhelming for us. The extended delay has resulted in the loss of our rent payments, and we continue to face immense pressure. Furthermore, the lack of responsiveness, refusal to answer calls, and the use of vulgar language when confronted is making this situation even more distressing. We have paid nearly 9 lakhs to this person, but have received no satisfaction, proper work, or quality in return. Instead, we are subjected to abuse. Additionally, they have threatened us, claiming to possess videos of us, and suggesting that they can harm us as we are families. They also possess one of our three keys and have not returned it to us. Unfortunately I don’t have any agreement with him as he was a reference given by one of my old colleague. But I do have online transactions of cash paid along with WhatsApp chats. Please suggest.