Builder installed patio door opening and made the floor above it sink! Advise please!
As you can tell from the title, we had builders create an opening downstairs in the kitchen to install patio doors in England. They created an opening and installed a steel beam according to a structural engineers calculations and this was approved by the council. We paid for the work but a week or so goes by and we noticed a few defects. Firstly the bricks were cemented in messy, but most importantly we move the boxes from the room directly above the kitchen where the opening was created and noticed that the floor has sunk by around 2 cm! We have hired a structural engineer to produce a report who said that it will likely be necessary to have remedial works to lift the floor back up to where it is supposed to be, but we have not received the report yet. The builders seem to be trying to deny that it was their fault but it very clearly is their mistake. Luckily, they are being cooperative and have shared their insurance details with us. Once the structural engineers report comes back, what should be our next step? Do we have to give the builders a chance to put it right? Naturally, we are very very hesitant about having the same builders back in who created the problem and do not want them touching the work any further. Is it possible for us to refuse remedial works from the builders themselves, in favour of other builders? Do we share the report with the builders or go directly to their insurance provider? We have paid for subsequent work such as plastering and patio door installation which will also be damaged in the process of remedying the sunken floor- will this be covered to be put right by the builders insurance provider?
Any advice about next steps is so greatly appreciated as we are stuck on what to do next!