Hello,
The franchisee shouldn't be able to log in to the GoCardless account. The GC account should be held by the franchisor and operated from a non trading central bank account which is used as a landing account for direct debit payments only.
The franchisee's then invoice the franchisor as required for the GC payments. The whole idea of a central bank account is so you can move jobs between franchisees easily and you don't have any bank details to keep changing.
GoCardless customer service has always been good for me.