This likely happened because you are on a yearly billed monthly subscription that hasn't completed its original billing term.
For a yearly billed monthly subscription, your plan will be discounted once the original billing period is completed.
For example, if you accept the cancellation discount on your subscription in month 3 out of the initial 12 billings. In this scenario the plan will not get discounted until month 13.
This is because the yearly billed monthly plan is an annual commitment, as shown on the pricing page:
