Another happy user here. Just got a package from them yesterday in fact. Running a repair shop on the side, I have ordered a lot of strings from them. Whenever I've talked to them on the phone, they've been nothing but courteous and helpful.
There was one time when I got a dead B string in a Fodera set. I found that JustStrings follows the manufacturer's policies. So in that case, I had to contact Fodera to report the faulty string and request a replacement. Every company does it differently though. A few months after that, my friend got a batch of dead D'Add's (guitar strings) and
JS sent him replacement sets for free, no questions asked. I would call them up and see what they say.
Whether DR QC messed up and put an E in a B envelope or whether JustStrings' QC messed up, you should get your due whether replacement or refund.
I deal with Sandra Hardy the most. Here's her info.
Sandra Hardy
Customer Service Manager
(603) 673-1104
(800) 822-3953
sandra@juststrings.com