Can’t receive calls from a certain number

[Alkav12]

My sons school have been trying to contact me but always gives an engaged tone. They have tried multiple times on different days and I still can't get the calls. I was not on the phone at anytime they tried to call. 
When I called sky they advised me to get a new sim which I did but still doesn't work

[caesarome]

@Alkav12 

I have escalated your post to Sky who will be in touch with you regarding this via a blue bubble which will appear at the bottom of this page.

This link explains how this works:
https://community.sky.com/t5/Did-you-know/Escalating-a-post-to-a-Sky-expert/ba-p/3711147

When the blue bubble does appear you have 48 hours to respond or it will be automatically closed.