Why are my apps and browser not working on mobile data?

[AC Question]

I have sufficient credit and my sim card works in other phones perfectly. When on mobile data I still receive notifications and am able to use fb messenger and whatsapp. My browser and apps won't load anything at all even with good service. The phone was purchased in the UK, is unlocked. I am in Australia with an Australian sim. I had no troubles last year but have recently returned from 6 months in japan. During that entire time I did not use mobile data, could this have something to do with it?