Yeah they just got back to me and told me to take my receipt, take a few pictures and a water sample and they will "sort it" for me. I am not sure what tests they use but if its the API kit then they are only gonna get the same reading as I am. Cool if they can offer replacement fish but not going to be much use if they are just going to die again.
They probably use something similar to test. As you say, it should be the same which means you'll get a few more fish. If you've ruled out your set up as the problem then getting different fish might make a difference.