Landline not recognise 0300

[manglesmum]

Trying to get through to my landlord to report an issue but just get the response that the number isn't recognised. Tried on my moblie - which I hate using- and it worked. I have seen this subject has come up before but has been archived so wondered if there were any more up to date responses.

[caesarome]

There have been some issues over the last few days with Sky Talk so can you make calls to other numbers or is it just this one to your landlord that you can not call ?

[manglesmum]

My landlord's a housing association. There are 2 numbers both 0300. Other numbers, either mobile or landline seem ok.