I believe that is an old grandfathered package. You could possible downgrade to 10 / 1 75 gig. Try inputting your postal code here and see what is offered.
Unfortunately, there are no options with that modem. I mean, I hope Marc will change his mind and offer a Lite plan on Cable 25, but we can't blame him if that just doesn't fit in the numbers.
Of course your modem is perfectly capable of handling Cable 10 or Cable 30, but it wouldn't be officially supported. Worse still, Rogers knows that your modem's MAC address belongs to a SB6120. So, you'll have to change your modem to change speed at all (or usage level, except switching between Pro and Unlimited).