It may also be an aerial problem. 4G only works close to a 4G tower, and drops back to 3G when the signal is weaker. The first way to test this is find a cellsite with 4G, park beside it and see whether your phone gets 4G...If it does, then we know it is a signal strength problem, not a band problem.

If your phone's aerial is making a bad connection through the charging board, the signal will be weaker....

Download an LTE coverage app to find a 4G cell.

Thanks Admin It works I put only one SIM and restart the phone. It shows full 4G Network. Thank you very much