I’m unable to text one of my contacts

[Spider14]

For the last week, I have been unable to send a text message to my friend (also in sky) she can text me, but my messages won't deliver to her. 
also I am unable to ring my son and when he rings me, it says number unknown. 
can anyone help please? 
it's driving me crazy 

[caesarome]

Has it been working prior to last week ?

Have you tried deleting your friends number (make a note of it first), reboot your phone then set it up again a contact ?

When you ring your son what is happening ?

[Spider14]

Everything was working fine last week. 
when I ring my son, I press the call button, his photo shows up and then it goes off.

I have tried resetting my phone, my network settings, have taken my sim out and put it back in but nothing is working.

my friend can message me but I can't message her.