I'll share another way so you can request for cancelation of your QuickBooks Cash account.
Please ensure your QB cash account has a $0 balance. You can either spend it or transfer it to your external bank account if it has a remaining balance. After that, you can call the number at the back of your QuickBooks Debit Card.
Since the number doesn't work, I'd recommend reaching out to our Payments Support Team. They can access your account and review it. Also, they'll be able to help you close the QuickBooks Cash account.