Ok....sorry, I skimmed it, not going to read all that.
I gather you do have combined billing. It saves you $120 per year ($10 a month discount). But creates the headaches you are experiencing. Prevent buying new phones, paying off Next buying phones from other retailers like Best Buy.
Unified billing is something they did after buying Direct TV. The two companies are not playing well together and not working as one. Yes, it's a nightmare for wireless. No, it's not worth $120 per year.
To simplify your life, have accounts un combined. This will stop the problems you are having with wireless.