Hi, I also had this phone before, and had the same problem as you, because I bought it online, I consulted the customer service, he gave me the resources below, you can try them.
Enter a "dual SIM settings-settings", select the section of "dual SIM open" then click "OK" Finally, restart the phone again.
2 close the phone, and return the card, then insert the SIM card with the correct direction after explaining slot. Finally, start the unit. That's it.
Hopefully, these resources can help.

contact with service centre

[Lang = en] Mon H168 phone identifies the SIM card No, cause there is no signal, je ne can not tel # & 233; phoner mainetenant, make a comment? Help me, please [/ lang]