1571 not working

[#1]

I had a missed call yesterday and I checked to see if they'd left a message. Intermittent dialling tone so clearly there's a message, but when I dial 1571 the line remains silent. It doesn't seem to connect. It was working fine up until this point. Any thoughts?

[#2 · Accepted solution]

Now appears to be working again all of a sudden after receiving a call from a with held number which I didn't answer. Never answer calls from numbers I don't know as I get an awful lot of them - at least two a day and they're always cold callers or recorded messages!