Phone not registered to a network

[kmc]

setting up my new phone and sim. Have transferred all contacts, apps etc but when I try to make a call, on either my old or new phone, both say phone not registered to a network. How long should it take for my new sim to activate and does it mean I cannot use my old phone/sim why this is happening?

[MI5 · Accepted solution]

@kmc 

If your old SIM isn't working too it means a transfer has started.

You need to keep rebooting your new phone.

If it won't come online after a few hours, you need to call customer service Guide: Coronavirus Community Help and Support