Theft by heat tech plumbers

Bought a heat tech geyser two years ago, geyser started leaking around the gasket contacted the company. They sent out a plumber to check the geyser, who stole the rewards sticker from the geyser and told me it's not the fault of the company. My private plumber had a look at the geyser and told me nothing was wrong with the connection. I think this company does not stick to their promises. They employ *******. I contacted the guy who came out immediately after he left about my rewards sticker and he refused to come back to return it. I think this company should be held responsible for what their staff does. They refuse to replace my geyser.