Using voicemail whilst abroad

[#1]

As the title suggests, I'm struggling to reach the voicemail centre whilst in Greece. Usually I just tap the notification, but nothing happens and I get cut off. I've tried searching on here and tried 555 and +44 7870020555, dialling my own number, even 1571 but nothing is working.
Any suggestions welcomed.

[#2]

Unimpressive service Plusnet!

[#3]

I don’t believe 555 would work from abroad nor would 1571 as that’s voicemail for a landline. 

00447870020555 should though. Do you have roaming turned on? Can you call other numbers?

[edit]

Reading Here not all roaming carriers support our voicemail service so worth bearing in mind. 

[#4]

Hi Gandalf, roaming is on and I've always been successful when just clicking on the notification. For some reason it just will not connect using any of the numbers or methods I've mentioned. Calls and texts are working fine.

[#5]

Time to give up. Plusnet clearly aren't going to help me. Embarrassing customer service...