Extract from the Terms & Conditions (September 2021):

1.4 Modification

ConvertiblePDF may modify, update or discontinue the Services, Software (including any part or feature thereof) at any time without liability to you or anyone else.
If we discontinue a Service in its entirety, then we will provide you with a pro-rata refund for any unused fees for that Service that you may have already purchased.

6.3 Billing

We will automatically bill your plan membership fee, price and selected payment method until your subscription is cancelled or terminated. If you do not terminate your subscription, it will automatically renew.
You and ConvertiblePDF may cancel or terminate your subscription at any time.
Any cancellation will take place from the next billing period, i.e. any cancellation will only cancel future invoices.
We do not provide refunds, except where required by mandatory law or where otherwise explicitly communicated to the user.
All fees are exclusive of any taxes, levies or duties imposed by taxing authorities, and you will be responsible for payment of all such taxes, levies or duties.