Can't activate voicemail

Hello all,

I hope you are well.

I am having issues activating voicemail on my Smarty. Namely, I have tried following instructions on the page "activate voicemail" by calling 123 (I also tried calling the international number, as I am in Europe currently), but I am immediately met with "First, call us from your mobile phone. Goodbye" and then it automatically hangs up. I AM calling from my mobile phone, the phone that has the Smarty SIM in it, so I have no idea what to do. All pages I can find on activating voicemail say I should just call 123 or the international number, so I have no idea if anyone else has had this issue before or how to solve it.

I have a voicemail waiting that is most likely professional, and I had no idea voicemail was not active before receiving it. Does anyone know if there is a way to activate voicemail other than calling? Because for some reason, the service is convinced I am not calling from my phone.

Thank you in advance for your help,

Eli