I have the same problem. mine goes like this.
I have a Samsung galaxy on 5 which was bought from metro pcs in USA and I think it’s a T mobile nationwide that was using on it before
So my uncle brought it to Nigeria so I inserted my Airtel network SIM card here in Nigeria inside it but it was sim lock
So I tried to unlock it and I was ask for my IME number so after for some days it was unlock
So anytime I put it at 3G it off the network but if I put it at 2G it works but you know how 2G network browsing is very slow
So what am trying to say is that 3G and 4G does not work on the phone with all Nigeria network provider
It only 2G that works with it
It shows E on top when browsing and sometime G I have to sleep and wake up before a site open.
what I also want to know is that is Samsung Galaxy on 5 a 2G or 3G or 4G phone?
Kindly please help me with what I can do
Hope to read from u soon