I have news on the matter!
Yesterday I went to pick up my phone, after last week the issue was not solved after the second attempt and they said they will try it a third time. (I tried to pick up the phone on Friday, but they were in the middle of a flee market and didn’t have my FP at the shop, when I came there…)
Long story short, the USB connector is not loose anymore (at least for now)! 
They told me that they could sand the junctions of the USB connector on the motherboard and were then able to solder in a new generic Samsung USB connector.
I’m confident again that my phone will work until January 2018. 