I have been involved in the trade for over 13 years,
I know offer a supply only or a supply and fit services you can visit the website for any products we sell
Very sorry to hear what you gone through, i feel you initially need to call the guy and have a sit down, and discuss it vey carefully as emotions could on whole make things even bad.
see what the guys have got to say and ask the questions directly, i don't see you with any rights here part from asking for the job to be completed as soon as possible and asking them firstly for you home back.
Yes all cost should be explained over the phone, and you then have the option of going into a verbal agreement when the trademan arrives.
You could just have a loose connection in one the sockets.
Best fuel saver is the traditional system rather than the combo, with combo start to become difficult when wanting ensuites with good flow rates on shower, with the combos always will have issues when drawing more than one tap.