I think you have a valid complaint to the manufacturer about the performance of your plumbing products. I'd take it up with them, maybe have them send a rep (other than this guy) to check the product or installation. I had a problem with Kholer (sp?) before. The first guy that came out, from the company that insalled it had nothing but rude and nasty to say. I politely thanked him and personally excorted him to the door, after making certain that he had all his tools and possessions in order.
I called Kholer (sp?) too lazy to go check.... and they sent a rep over. He dropped some dye pills in the tank and noted that a ring was installed backwards which caused my particular toilet to flush with so much pressure it would splash over onto the floor every time. He dis assembled a thing that sounds nasty but it's really what it's called. (ballcock) unscrewed some screws, flipped the pressure washer over, and fixed my problem) all this took was a call to an eight hundred number.
Why was I polite to the first guy and not fly off the handle or stoop to his level? Basically, he knows where I live. My name and phone number and credit card number if he wishes to dig further. So biting my tongue till it bled (I really wanted to put him in his place) I was nice and polite and thanked him for visiting and payed 35 buck fee.