I've had mine since Nov 2020, no issues with deletion. I think the trick is to have a CC on file or be charged at least one. I know I generated a few storage charges, ended up paying less than $2 but I think that has classified me as a 'paying customer'. However I would recommend always being prepared for eventual deletion. Make backups, record your process for setting things up so you can switch to a different provider should the worst happen.
They're 12-24, we use these at work.