Phone gone crazy - Note 4

Ok long story here but necessary I believe....

Bought the phones (yes 2) in November 2014 (T-Mobile 2-year plan). Loved them. Easy to operate, pretty fast, always responsive, take abuse (with decent case), and just overall great..... Till about three months ago.....

The first one started having charging issues.... Ok, no biggie got get a new battery. Then the new battery was apparently drained in 30 days! Ok, we have a problem.... Put in the old battery and now no issue.... perhaps hangs up a bit but usable....

The second one started having issues as well so just went and got new battery to be prepared.... Ok, install new battery..... Hanging up..... shutting down for no apparent reason..... calls dropped..... Screen unresponsive.... will not power up..... will not power down unless battery removed...... will be on charger and not turn on..... or be on the charger and not power down...... round and round....

Ok so research..... talk to T-Mobile.... No one can seem to find an answer - Hard Reboot it freezes in the middle (24hrs). Take out the battery and start again..... Then the Phone starts buzzing / vibrating while NOT turned on.... so take out battery and IT IS STILL VIBRATING!!! ok so this is beyond weird..... There is just no consistency with the issues and from my perspective no apparent reason for the issues.... and before you go with infection from apps or malware checked that as well.... nothing.....

So the situation now is this...... The second phone (the one that is acting like it is possessed) is operational but slow, screen intermittently responsive, dies for no apparent reason, will sometimes take a charge and other times not. The first phone is very vital to the person who uses it (must have for work daily).

I really liked the phones when they were working and I would love to get them repaired. Can someone please help?