My thoughts.... SUE THEM! Really, sue them in small claims court. First write them a letter and send it certified return request and tell them to find out what other than you is causing the problem and fix it or you will sue them after 30 days. And then do it. If they say it's the volume of water you use, that is their fault then for not sizing the equipment correctly; or if the equipment was there and they didn't sell it, they should have told you it was too small and they should have walked away unless you bought larger equipment.
They do not have the order of the equipment right and you shouldn't be softening irrigation water, as you see, it doesn't work and you'll probably end up killing the vegetation because of the added sodium; which with 9 ppm of iron plus whatever hardness, is very high. 7.85 mg/l of added sodium per grain per gallon of ion exchange with 4 gpg per ppm of iron alone = 36 gpg plus the hardness and 2x the manganese if any.
Chlorine first, properly sized retention tank, backwashed turbidity filter preferably Centaur carbon to remove the chlorine and clarify the water, AN filter and then softener.
And get the irrigation water before any equipment and use an iron filter or polyphosphate feeder that will sequester the iron on the zones where the staining is a problem; or better yet, tear out the grass and plant stone, mulch etc. or allow nature to take control.