I've been charged for five international text messages and I am fully certain that I have never sent them since I only use chat apps like Whatsapp. My phone's also not an iPhone so it's definitely not one of those iPhone-related issues.
Can anyone please help me? The staff at Optus said they couldn't even help me with this and I needed to contact customer support. Yet customer support said they could only deal with urgent service matters. This is urgent for me because I'm due to pay the bill in a few days. Cheers.