Wish I could give no stars. Absolutely disgusting ...

Wish I could give no stars. Absolutely disgusting service after installation. We live in a property owned by family. We moved in February 2018.
In 2016, the original owner had a battery system installed by Gavin Goodhew at Goodhew Electrical & Solar. The original owner of our house was in his 80's and passed away not long after installation of the battery system.
We contacted Goodhew Electrical & Solar in April 2018 after receiving a very high electricity bill. It was evident the battery system was not working. It took over a month for Gavin Goodhew to come out and look at our battery system (after he sent someone out who wasn't even qualified in battery systems?!). We were then told Gavin was the only one qualified to work with the battery systems. Gavin reset the battery system and installed updated software. We thought it was fixed.
In October we received our next invoice from our electricity provider (they were late in providing invoice). We graphed our bill to try and understand where the cost was coming from. We were receiving a rebate on our solar, which means the solar energy was not getting stored for our home use. The system was still under warranty.
We contacted Goodhew on the 29 October 2018 to fix the issue. Since then, they have made no attempt to rectify the issue and the owner Gavin has ignored all our calls and emails.
We have since contacted Office of Fair Trading. Goodhew have not agreed to fix the problem or talk in mediation.
Apparently it's because there was a verbal agreement with the now deceased owner, that because he (apparently) got a good deal of $12,000, there would be no warranty on the system. This is not legally binding.
Gavin claimed he came out multiple times, he came out ONCE!
My partner commented on their Facebook, conveniently they were deleted. They were just honest comments about what happened to us.
AND.... Love how they're using photos of our house to sell a battery system that lasted less than 2 years.
AVOID this business!!!!