I can see my colleagues from the case management team have emailed you this morning to check that you're now opted out. If you need further support you can reply directly to their email.
Further to my post above:
My understanding is that BT Wholesale buys access to the physical network that Openreach runs and manages. As you say Openreach manage the equipment, not only from the cabinet, but remotely from their network management centres as well. Whatever the commercial and network management arrangements, cycling the WiFi opt-in/opt-out fixed my issue.