Incorrect Installation refusal to fix

I had a incorrect fibre installation from VOX, I tried for Months and months to get them to come out and fix the installation, Eventually I placed them on breach of contract and they still didn't come out and repair which lead to my cancellation of contract, They collected their router and now want to charge a almost R3k cancellation fee even though they are in the Wrong. I have e-mail strings longer than the Nile and now they don't reply just keep sending invoices and their accounts department doesn't reply either??? Worst Experience I have ever had with a provider. Stay Far Away, I looks like I'm going to have to go the legal route