I have found Koofr but I want to see some more to compare prices. Someone mentioned Sync but it requires KYC or at least when paying they ask for all details.
Also, what happens to your files if you forget to pay? they delete them or they keep them? I have never used this.
As for Koofr, I found on their website that they accept payments by Braintree and Paypal, but I did not find the option to pay by Bitcoin:
Subscription fees are paid in advance for the specified period and must be made via credit card, PayPal® charge or invoice, and your subscription will not automatically renew. All payments are processed via Braintree and Paypal.
https://koofr.eu/tos/As for files, they say that no data is deleted, but premium features are disabled until you upgrade or pay:
If you do not renew the subscription, your account is automatically converted to a free account, which means the quota is reduced to 10GB (no data is deleted) and premium features are disabled. You can upgrade again at any time. If your account remains over the quota for a longer period of time, we may ask you to remove some of your data or the data will be automatically removed.
https://koofr.eu/tos/