I feel your pain, but I don't think it's as bad as you state. I've had to call in many times (maybe 4 or 5) over the years to "reinstate" my modem as customer owned. This happened especially when I've changed promotions, which seems to delete the customer-owned modem. In all cases, I've never had a problem getting my modem quickly changed back to customer-owned.
My view on this is that Comcast would have to prove that it is their modem. I'm innocent until proven guilty. So far, I haven't had a test of this view, since Comcast has quickly fixed each problem.
As far as credit card/banking information, I've been on autopay for at least the last 8 years, with never a problem. You may have had a different experience, but it works for me.