It doesn't matter that you haven't made a sale; the refund is based on whether or not you've used any of the tools of the Professional account:

I did not use any tools and want to end my Professional selling plan. Will I get a refund?

You are eligible for a Professional selling plan refund if you have not used any Professional tools or benefits after signing up. If you want to end your Professional selling plan, you are eligible for a one-off refund of up to three months, and your refund request needs to be initiated within 90 days from the payment date of the Professional plan selling fees. If you meet this refund criteria, contact Selling Partner Supportfor assistance with refunds.

If I did not generate a sale, am I eligible for a refund for the most recent charge?

No. The subscription fee is charged for the use of tools and benefits. We do not issue refunds based on your sales records.

If you haven't already, downgrade to the Individual Plan first, then request the refund if you qualify.