1. Have you already paid a substantial sum to the contractor for the work?
2. what percentage of work in your assessment is still pending?
3. are there any email correspondences or sms or whatsapp chat exchanged between you and the firm wherein the firm has promised various dates for completion of work?
4. have you assessed the track record of the firm from their other clients whose works the firm undertook and successfully completed?
5. are you out of your home right now or required to pay rent for alternate premises pending completion of the interior work?
6. based on the above, you may consider issuing a formal legal notice to the firm. But prior to that just have a plain curtsey letter smartly drafted through a lawyer so that you can ascertain whether the firm is giving you empty promises or is actually driven to complete your work. I am saying this because a legal notice may have a negative impact on your work and there would be bitterness between you and the firm which may spoil your interior work
7. so in all i suggest you shoot a curtsey letter for now and if by the next promised date, the firm still fails to deliver then you can consider legal action