You can just let the subscription expire. The subscription do not auto-renew. If you do not take manual action to renew them they just expire.
If you don't mind me asking –and replying to this is totally option– what is the reason you want to cancel the subscription to Akeeba Backup? I am only asking because I see that you've been a subscriber to it for ages. If it's a temporary issue on your end we will be very happy trying to do something to help you, e.g. an extension, an extra discount, or giving you a coupon so you can reclaim your renewal discount if you are planning on returning a few months later.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!