Switch from BT Infinity - equipment

[#1]

If they are already on Sky FTTC, there's nothing for the engineer to do in the cabinet, it's already connected. Probably Plusnet have booked the standard managed installation with Openreach modem, and it's been cancelled by Openreach once Openreach realise they already have FTTC, so there's nothing for an engineer to do. And Plusnet don't seem to be aware that it gets cancelled.

[#2]

You are 100% correct, of course.  I missed the SKY Fibre bit.  Yes, in that case I suspect someone at PN has just been running on automatic and not realised the user already had fibre