Heres a few tips bro. Make sure you "start a new story" and not just change the difficulty to hard and start chapter one. That won't work. You have to start a new story and select the difficulty from there.
If you only go to the options and select hard mode and jump into an already played chapter, it won't work. I tried this myself. Starting from scratch won't force you to lose any of your achievements nor disc upgrades, etc. Only the chapters will be renewed and forced to start from the beginning. All other chapters will be erased until you beat them one by one again.
If you did do the above steps, then I can only imagine its an error or glitch. But try what i suggested above first. See what happens.
