Puritech poor after sales service

If I could rate 0 stars I would. As a certified installer of water purification provider one would expect them to know what they doing and be upfront and transparent. Post installation it came time to change the filters. That's when I realised no non-return valve was installed. As such I wasted kilo-litres of household water that drained out my home before I could change them. I contacted them at this point only to be told I should have asked. The manage Christine refused to contact me and put me on with multiple technicians who refused to acknowledge what I was saying and said verbatim that they didn't want to be accountable for a valve installation as they didn't want me to contact them if anything went wrong. So I must ask at installation, not being a professional, but they won't assist?! Makes no sense. The after sales service is pathetic and this has not been resolved or received requested contact from Christine the manager.