New build nightmare (barratt david wilson) what should we do?

To cut a long story short, we purchased a newbuild from Barratt David Wilson (BDW) in 2025, which was so awful that they ended up buying the house back. We were then offered an alternative property with many assurances. We paid over 900k. So far, we have found issues with debris and rubble in the garden, faulty boiler, a leak, faulty driveway, multiple issues. BDW are not being receptive and ignoring multiple issues.
In terms of legal action as far as we are aware we have to let them answer the complaint first. What is a reasonable time frame to allow for resolution before we go to court?

Also, never ever buy a David wilson house!