Warranty Voided

Our burst geyser is 6 yrs inside the 10 yr warranty period - however Duratherm claiming the installation is non compliant!? Every day they have a different reason why they can't honour their warranty. Based on reviews on this site, and what I am hearing from our plumber, it seems Duratherm are voiding warranties on technicalities. Our installation was done in 2011 as part of the Eskom subsidy, by a reputable installation business! And the inspecting plumber (independent to Duratherm) informed me that the burst geyser was compliant. They never phone back, they do not answer emails, they keep you on the line forever.