I didn't have to contact anybody. Ray at Reef Supplies sent me a link to Hanna's website and I just put the lot number in. (Ray looks after his customers!) It said my tester was one of the lots affected and I just had to enter my mailing address.
This is the link I was given if it helps:
https://hannainst.wufoo.com/forms/w1hzjs2j1b4ejyu/