While I'm one of Seachem's biggest cheerleaders, I'm not crazy about their ammonia test.
Having said that, I love all their other tests, and once a tank is cycled, there isn't really a need to test for ammonia unless a problem is suspected.
I've used their test kits exclusively for well over a decade.
A bought their Nitrite/Nitrate test kit earlier this year and the Nitrates have never registered. I had to fall back to an old API kit to get through my cycle. Pretty sure I just got a bad kit. The Nitrite test seemed spot on. Hunting for a new Nitrate kit now.
Why do you think you got a bad Seachem kit? Did you test the reference solution to check? That will tell you for certain, either way.
In the unlikely event that you did get a bad Seachem kit, call 888-Seachem and give them the lot numbers from the reagents and they can confirm if there is a problem with the lot, or help you with your testing method, or replace the reagents if they are bad.