I've been using Jelly Pro well since the beginning of this year.
It is an MVNO company using KT network (3G) and is located in South Korea.
The APN settings were adjusted exactly, so I was using it well.
About two weeks ago, I updated Jelly Pro to Android 8.1 using System update of the device itself.
Immediately after the update, the device will not be able to connect to the network.
Not all calls, SMS, DATA, etc. (Except through Wi-Fi)
After the update, the APN settings were re-adjusted correctly.
The USIM has been newly issued through the carrier and I have tried to replace it, but it still does not work.
However, if I use another company's USIM with Jelly Pro, it will work normally.
The network used by that USIM is also from another MVNO company that uses the KT network. In this case, LTE(4G).
I asked the carrier.
Then engineer says it can be used in WCDMA mode.
It is said that it should be converted to a mode such as "WCDMA all" or "WCDMA only" or somthing like that.
I would appreciate it if you could tell me how to use Jelly Pro again as before.
p.s. This is a sentence written using a translator. Please note that the text or meaning may not be smooth.
Please try to give a substantial answer. If you wanted to comment on the question or answer, just use the commenting tool. Please remember that you can always revise your answers - no need to answer the same question twice. Also, please don't forget to vote - it really helps to select the best questions and answers!