Plumber incorrectly installed kitchen drainage pipe

Hi guys,
I am here today to seek your advice. Sorry for the long post, I wanted to give as much detail as possible to explain my problem. My home is newly built and completed in Oct 22, I moved in on 12 Oct 22.
On 29 Dec 22, I noticed my kitchen cabinets warping and a bit of mould near one of the skirting boards. I suspected there is an issue and called my builder. Note we were still in the 3 month warranty period.
They were all going on holidays and told me I had to wait or get a plumber to come out myself. I was hesitant as invasive works would be required to see what is going on under the cabinets and may affect my warranty with them.
Anyway their plumber did come before on holidays, found that the drainage pipe of the kitchen sink was incorrectly connected to a conduit instead of sewerage. Therefore, this whole time since installation, but mainly since I started using the kitchen all the water had nowhere to go and been accumulating under the cabinets, tiles, plaster, skirting, adjacent rooms' floorboards without being detected. A horrible thing to happen to any home. The plumber rectified the pipe connections and left.
I emailed the builder the next day asking for them to organise the house to be stripped and ventilated, but they said they are away and I need to wait till the 16th Jan 23.
On 5th Jan 23, I organised for.a water damage restoration company to come out, at my own cost, to examine the damage, report and quote.
On 16th Jan 23 I sent the report to the builder. They took a few days and asked me to start the works and to make the payments and I will get reimbursed. I declined and said no, you start the works as the house is under warranty and your plumber caused all this mess. After much back and forth, they came back later saying the plumber has decided to put an insurance claim to sort this mess. The insurer has advised plumber liability insurance takes a long time to process, and they have mentioned that I have a duty to mitigate losses and should consider stripping and ventilating and provide final amount of claim. I do not have such kind of money which is costing more than $10,000 dollars in stripping and ventilating alone. The insurer has not confirmed if they will accept liability yet want me to start the remedial works. Moreover, my house is under warranty and I really do not want to do things on my own given it can void my warranty on the house as well. The builder does not want to spend any money until the insurer has confirmed acceptance of fault.
Given the house is under warranty, should the builder be starting the works? However the insurer has not directed us to do so, stating it needs to be done at my own volition and expense, as part of my duty to mitigate. If I take an example of a brand new car under warranty, but faulty, the dealer would be organising all repairs, not me. But the builder is not initiating any remediation work, and on top of that, I am the claimant on the form as I am the owner of the house, even though the builder is liable under warranty.
What do I do?