Personal hotspot

Hi. How r u. My name. Maxi. And i would like to know that I am with Optus carrier and I try to use personal hotspot but every time I want to turn it on. It keep say to contact Optus. But when I call Optus they tell me to contact apple. Can u help me to get the personal hotspot on pls. Cause i try to use my ipohone 4s internet for my computer. But if i use vodafone carrier Or telstra carrier, I can use my personal hotspot no problem. Why? Can u pls help me to sort this out pls. Thanks u very much.