These threads are always difficult, there are two people involved and typically it seems like the whole story doesn't come out because it's not available or it doesn't help a cause.
Sorry you had a bad experience with UDP. I've heard of guys having the best possible experience and the worst possible experience at UDP and many other companies.
Companies live and die by their customer service, but absolutely when you're the owner you can decide what is worth your time to deal with. Sometimes the money a customer pays isn't worth the work to get the money. Not saying that happened here or not, but it's true. Many companies refuse to take money from customers who are just going to be more hassle in the long run.
As for your adapter, quite a few other companies sell them including ATPTrucks and Copperhead Diesel. ATPTrucks.com is a vendor on DD even, that's who I bought mine through.