Do you fill in the defect form? If yes you are required to sign off after the defect is repaired . Since the defect is still there you have the right not to sign off and request them to repair again . There is last withholding sum held by the lawyer so if the defect is not repaired you can ask the lawyer to pay the cost of repair to you, Refer to the thread https://forum.lowyat.net/topic/385900 for more information.

Doesn't matter, you can still raise a new defect form even after you already signed off. Their lawyer also need to act on your instruction since your right is provided in the S&P.