Product and service is appalling.

I've been having a minor issue with my car. Loses about half a litre of water every 1000 kms but still drives 100 %. Did some researching and it was pointing to head gasket. Checked online n found a local product "gasket magic". In About July last year I gave them a call n explained my situation. I spoke to Koos, who then was extremely helpful. I did inform him that I had added a bottle of aqua clear, which I do to all my cars as it keeps the cooling system clean. I was convinced that I was making the right decision. Got the product a day later. Called Koos again before adding the gasket magic. To have peace of mind I flushed out my cooling system a few times. I added the gasket magic n "wallah"..... All my problems started. This so called Magic has blocked my cooling system. My car began to heat up, loses water every 100 kms. Heater blokes cold air even when car is hot, I mean really hot... I wasn't sure what I did wrong as I followed the instructions with a magnifying glass and only after consulting with Koos. The low water warning comes on even if the water is full.. I called their office and spoke to Yvette as Koos wasn't available. I explained to her my situation. Koos has never once contacted me. I've called the cell number and left numerous messages but still no Koos. Now they don't even take my calls so to me I've learnt a valuable lesson that there are no short cuts. This product sounded too good to be true and I regretfully found out why.