Voicemail inaccessible from Japan

I am based in Japan. I have topped up GBP 10 to be able to call.

I cannot listen to my voicemails because not pincode was setup.

Calling either +447782333123 or 123, I hear 'first setup pin on your mobile phone, to do this call us from your phone" which is exactly what I am doing but the call is not recognised as being from my Smarty phone number. It is from the Smarty phone number not my japanese line.

Any solutions to be able to call +447782333123 or 123 from Japan and be identified as call from my own line?

Thanks