Dead after repair shop battery replacement

My iPhone 6 had a non OEM extra capacity NOHON battery in it for over a year when it started requiring multiple charges a day as it would shut down at 50%, then 60%, then 70%. Then I noticed the battery was so swollen it was trying to break out of the phone casing.

I had another NOHON battery lying around, also for over a year, purchased at the same time. Because I’m no professional and wasn’t sure if handling the swollen battery was safe, I took it to a repair shop.

They put the new battery in and gave me back a dead phone, saying the charging chip must be broken. Since repairing that would require it to be shipped out for a week and would cost more than the phone is still worth, I took the dead phone back home.

There are files on the phone that I need, as well as my 2FA app Authy. iTunes doesn’t recognize it.

It was working and charging before I took it to the repair shop. Did they just break my phone? Is there a fix?

UPDATE:

Back home I hooked up the faulty swollen battery again. The phone does charge and boot with that one. But the repair shop said they tried one of their own batteries with no success.