There are three options... you do have to search for the options when subscribing
Annual plan with one annual payment... I think there is a penalty if you cancel early
Annual plan with monthly payments... there is a penalty if you cancel early
Monthly plan... cancel at any time with no penalty
The PS+LR plan is $120/year either one payment or 12 monthly payments of $10, no ad hoc monthly plan.
The Single-App plan (PS for example, but doesn’t include LR) is $240/year either one payment or 12 monthly payments of $20 or ad hoc payments of $30/month for as many or few months as you want.
The All-App plan (PS & LR & 20+ apps) is $600/year paid as once payment or $50/month, or ad hoc payments of $75/month for as many or as few months as you want.
It’s all on the Plans page if you change the various options: https://creative.adobe.com/plans
Will I be able to cancel the plan without being billed the price of the months I haven't used within that year in this case being 9 months?
You will be billed for 50% of the remaining months e.g. 9 months for the photography plan = approx. $45 extra.
See section 1 (5) at the link below: