ᐅ The plumber keeps rescheduling every appointment and has stopped continuing the work.

How should I properly respond when a plumber has been delaying a new build for months? The plumber accepted the contract and, in the presence of witnesses, stated the work would take two weeks. Now, 14 weeks have passed and only half of the work is completed. Other tasks on the construction site cannot proceed, and the schedules of the other trades are being pushed back. I have now been informed that the work is expected to continue in about five weeks. However, based on experience, I expect this date to be postponed again for some reason. What is the correct legal way to handle this?