Ipad Pro - Sim card not working after update to ios 15.7

Since updating my iPad Pro 11-inch 1st Gen to iso 15.7 my PlusNet sim card used for data is no longer working. The sim card worked previously to the update as have other sim cards I’ve used in the past. I am now at a loss as to why I can no longer use my sim card on this iPad so I’m appealing for help or

advice as I’ve drawn a blank.

I have tried all the online suggestions I can find like

a) Switching off airplane mode waiting and switching it back on.

b) Resetting the Network Settings, location & Privacy, All settings

c) Cleaning and Re-seating the sim card.

d) I have not been prompted to update any carrier settings when returning the sim card to the device.  

The graphic option to turn the Mobile Data On or Off in the setting menu is no longer present. It only gives options to select a network provider Gigsky, RedteaGO, Truphone Other...   (see Pic 01 below).

I’ve probably never noticed before but could this be because my sim card is not recognised and is only present when it id's a sim card?

To switch the mobile data on or off I now have to ask Siri to do it or from the drop-down menu. 

In the about section of the settings, the Network Provider reads iPad 50.0 mobile data number Unknown.

I have tested the sim on another device an Android Phone and found it to be working. PlusNet report that there are no problems with the card.

I’ve tried another working Sim card on the iPad and found that that also didn’t work.

I have owned the unlocked iPad for 3 or more years and have used various sim cards from different networks all of which have worked. Including the PlusNet one which has worked up until this update.

Has anyone else come across this problem and is it a hardware or a software problem?

Cheers in advanced

Pic one