Scramble, good evening.
If your Insurer appointed the builder, then simply go back to your Insurance Company and tell them the workmanship is simply not acceptable and tell them to sort out their preferred Contractor, you did not choose the Contractor [or so it seems] the Insurer as above [appointed] handed to the Contractor your Claim to sort out.
Your post appears to infer that there were two independent Contractors? appointed by the insurer? am I correct?
There is a certain shall I call it Relationship? between Insurance Companies and the Building firms that undertake the work for the Insurer.
Bottom line is that if the preferred builder is not capable of sorting out the problem go back and demand the insurer makes his contractor toe the line.
As an aside take careful note of ant telephone calls, where possible use e mail [that way there is a positive record] at some point in the future it may be needed?
If when talking to the insurer they tell you to sort it out inform the insurers handler that you are now making an expression of dissatisfaction as regards the building work and the insurers attitude, then ask to speak with a Supervisor, at which time use the same phrase [an expression of dissatisfaction] Why? because under insurance Rules this is a first step in the complaints process that the Insurer MUST log and act upon.
Would like to know the outcome if you have time to tell the board?
Ken