Work left uncompleted and lack of interest to finish the job

I purchased a major electric work (R55000) at my property to get everything in compliance. This was done in January 2018. After they had done their work on an Electric Blind it didn't work any longer. When approaching Blackland for fixing the problem they said that they have left their electric business and sold it. However, my contract is with Blackland so in my view it's still their responsibility to make sure that the problem is resolved. I have been chasing Blackland as well as the new company since January with no success. I did the mistake and paid their final invoice which should be ok if you are dealing with a company that take the business and their customers seriously. Blackland obviously don't belong to that category.