Could you know the reason of 3G and 4G working but 2G is not working ?

[Windows Central Question]

I have Lumia 640 LTE. It was working normally then suddenly appears like I don't have signal when I check the SIM I found that the phone works with 3g and 4g but is not working with 2g.
So I can use data and calls by Whatsapp, Line etc... but I can't make a regular calls.

Somebody can help with this

 

[Chintan Gohel]

I have Lumia 640 LTE. It was working normally then suddenly appears like I don't have signal when I check the SIM I found that the phone works with 3g and 4g but is not working with 2g.
So I can use data and calls by Whatsapp, Line etc... but I can't make a regular calls.

Somebody can help with this

remove the SIM and put it back in (while phone is off)
Or get a replacement SIM which shouldn't cost much