Well, ARM is owned by GE Services, which is a pretty big, legal collection agency. So, ARM is legal, it's their client that isn't, because they can't provide all of the information to legally validate the debt.
teriahosking-You can wait until they send you to collections. I would file compliants against with the BBB, and see what happens that way. It's almost better to wait until it goes to collections, and then do the debt validation letter, as MTE will not longer own the debt, they will have sold it to ARM.