How to call customer services 4445 from abroad

[Classicus]

Hi, I'm new to O2.   I've got a sim card and topped up with £10. 
I am abroad, when I try to dial 4445 or +444445 I get the local service provider recorded message stating something like "you call cannot be completed as dialled".

What am I doing wrong?  I really need to speak to "Customer Services" to understand more about the Pay As You Go , and whether I can get a better deal.

Please help!

[MI5]

It is free from an O2 phone @Classicus 👍

[Classicus]

Thank you ever so much, MI5, it is understood and the issue is resolved.
With Kind regards.

[MI5]

@Classicus 

You're most welcome