New charging port flex, not charging properly

Hi, I am a novice in phone repairs though I have successfuly replaced the screen and charging ports on a samsung s6 and note 4.

I am requiring some expert advice on this problem, I was given an XZ from my friend with a cracked screen and charging problem, the charging port became temperamental and failing (at least I think it was that) and eventually wouldn't charge at all. The charging port was handled a bit harshly toward the end, for example the charging cable lifted up and down to try to get a charging response.

Anyway I ordered a screen/digitizer and charging port flex for it, and fitted them, following a guide. Before this, the phone had around 2% charge. After the repair, I switched it back on and conncted the charger, the screen was fine, however there was no response from the charger. The phone then ran flat and eventually ran flat enough to not be able to show the "low charge" symbol when the phone is off. Then after plugging and unplugging the cable (via USB in the pc) it would charge for what seemed a second then stop, the red charging notification light was lighting up. The same happened with a wall charger. I then stripped it back down and back together again. This time there was no response if I remember right, then I connected it to the wall charger and left it for 3 hours or so. I went back to it and it had charged up to 15%.

Now i'm at the point where the phone is working, it's on 90% now, but it charges very slowly, around 60-350 mA per hour on Ampere app. So a full charge is around 12+ hours. This is in the wall socket with a fast charger. Additionally, it takes 10 seconds for the phone to recognise the charger after is is plugged in and that is consistent each time I plug it in. The phone now isn't recognised by my PC via USB, and also won't charge that way also, it just doesn't do anything if I plug it in there. Other than that, the phone works and it holds its charge well.

Any ideas? Thank you.