VAT on Partial Solar Install

Hi, I'm the end user here, but thanks to the installer breaching the contract, I'm now having to deal with installers who don't know how I sit regarding VAT on my Solar Install. I signed a contract for the supply & install of a solar system in July 2022, comprising of Panels, Battery and Inverter. I've had the panels installed and battery supplied (but not installed) and the company I signed the contract with now have said they're not going to install the rest as the subcontractor they used to use no longer does any work for them and the new guys don't know the system that I want installing. So I'm now having to get quotes from other companies to supply & install the inverter, install the battery and commission the rest of the system. But there seems to be confusion over if this is VAT exempt as per the rules or not. Also, the previous installer has supplied the panels and battery at zero rate VAT, but according to the rules, because he's no longer installing the rest of the system, this presumably is now not covered by the zero rate VAT as it's not a complete system. Who is liable for the VAT that is now due on this, me or them? With the remainder of the system, there's likely to be around £2K materials cost and probably the same labour cost, but again, because this isn't supplying a full system, can they zero rate the supply & install of the rest of the system - remember, there are no panels required, so is just a supply of the inverter and installation of it and the battery. Any help would be gratefully received.

Hi,
The query appears to be a dispute between the end user and the installers and not an HMRC issue,
If there is a dispute regarding the liability of the supply between the various parties this is a legal dispute rather than a tax issue. 
With regard to the eventual supply by a new company, this would still be a supply of energy saving materials and can be zero rated.
Thank you.