Poor service from heat tech and it's service agent

A geyser within a valid warranty period installed in 2015 had it's warranty voided because the service agent found a one way valve in my yard and claimed that at some stage it was installed between the geyser and pcv. Heat tech then voided the claim even though that legislation came into effect after 2015! Further to this, the plumber was abusive, threatening and vulgar. Proof of which I submitted to heat tech. To date they have not responded to my complaint.