I need to cancel a subscription, but the system will not allow it?

Use the information here to contact Apple Support. If you are getting the buffering when going to Subscriptions on the iPhone, maybe you can see it on this link and handle the cancellation. Subscriptions and Billing - Official Apple Support

Why won't it allow it? What happens when you try to cancel the subscription? If you receive an error, can you please share the exact text of the error?