Phone does not charge. Problem in charger or motherboard?

Hello,

When I first bought the S6, I charged it to 100% and switched it off; but then I went to get a SIM card for it and tried to switch it on, it wouldn't. I went back home and charged it (turns out it was 0%) and everything was normal for a few months. The same phenomenon occurred again later. But that's not even the problem.

Usually, the battery takes a long time to drain. Before going to sleep, the phone was over 60%. When I woke up it was 20% only. That had never happened before, it usually drains by 5-10% or so.

I overlooked that and tried to plug it in to charge, but it wouldn't recognise that a charger was connected. I kept on trying until in 15 minutes, the battery died and the phone switched off and it STILL wouldn't recognise the charger plugged it. Note that this is the original Samsung S6 charger that came with it.

When it's switched off and I plug in the charger, it gets this primary sign that comes before it shows that it's charging, but then it goes blank again and it doesn't charge. It doesn't even show any sign of recognition when connected to the laptop.

I was very careful with the phone and I'm sure that no water got in. Perhaps there might be dust in the charging socket, but that's all. When I consulted the customer care they said that the problem might either be in the charging socket or in the motherboard. The socket would be relatively cheaper to replace but the motherboard is very expensive. I have a warranty in another country, but it'll take about two months to get my phone back.

I want to know, by what I've recounted, is the problem in the socket only or in the motherboard too?

And if a maintenance centre here opens the phone from the back to check if the problem's in the socket, will that get it out of the warranty abroad?

And if the motherboard is replaced/repaired, does this erase the data present on the phone?

Is there any mean to recover it?