sim cards and no numbers

[OdjnAltoro]

this is an utter nascence to be frank. the whole O2 sending out plastic sims with no number on them but the sim has a number you have to register. I've tried so many times it's getting beyond stupid. so much hassle to activate a sim card, i was got  given a black view a70 pro phone by jobcentre, so i can use their stupid universal credit system, and i ordered a pay as you go sim from 02, I've taken all the steps to assign the number to the sim but NOTHING and i mean ABASLUTLY nothing works, even putting it in my friends Galaxy phone didn't work.
yes i know my phone number, it sometimes gets text but mostly it dosn't. it's driving me crazy, as it keeps saying number unknown but seems to find everything else fine 
PS, yes it does have credit as i had to do all that during the sign up phase after getting the sim.

[OdjnAltoro]

PS yes i did top it up, there is credit on it's account. but still nothing works

[MI5]

@OdjnAltoro 

Apart from very old Nokia's, the only phones that can write numbers to sim cards are iPhones, however, it isn't necessary for the phone / sim to function correctly.

What exactly is the issue?