Thank you for reaching out to the Community, @liz-brown.
Before your client decides to cancel, we'd like to explore solutions to meet their needs. Our team is ready to review their account and discuss options. They can call us for free at 0808 168 4280 (mobile or landline).
Now, since you don't have an option to directly cancel your client subscription. I suggest to transfer billing to client option to remove your client from your Wholesale Billing and let your client perform the necessary steps because it's possible that your client is the primary admin.
I'll also add these articles for more insight on how wholesale billing works and removing a client or company.
Let me know if you have other questions or concerns about canceling wholesale client subscriptions. I'll be around to provide further assistance to you.