I am currently on a mobile plan $25 for 3GB. I would like to upgrade to a $35 plan with 30GB, and was shocked to find out I have to pay cancellation fee for my existing plan. I have always thought that if I am going on a higher plan ($25 -> $35) there should be no cancellation fee.
Has the online sales staff made a mistake? or is this a normal practice for Optus?
It just seems odd that I would like to pay for a more expensive service yet being denied by optus.
No mistake. You can only upgrade data amounts within the same family of plans. You can ask what the next level up is for your current family (CIS). Probably 10Gb for $40? Switching to the latest special promo offer isn't allowed, even if its more data.
Another option you might use is to get a second new mobile service (mate? family friend?). If its under your name then you pool the data and can share it.
That said, it seems strange you're up for 12 months of exit fines. Have you asked the actual amount as Optus usually cap the amount and also prorata the amount down the longer you have down the plan.