Was anyone elses mobile service automatically changed to the highest billing service when their promo 12M sim expired. It is not mentioned in the fine print and I was not advised this would happen. In addition I was slogged a $15.94 late payment fee because the bill was larger than my contracted amount!
Generally Optus just roll over plans as is to month to month. However more plans are getting 'bonus' components that do expire. Usually this is data but can be a discount that expired.
I expect you will find it's been mentioned some, possibly on the main sign up page. What cis are you on?
At this stage of say just start looking for a new deal with Optus or elsewhere. You could also try calling as an agent may just take the original deal on request.