I'm very confused by your post. Starting with the word "transfer".
I'm not aware that the Ofcom rules on an FTTP migration
are any different from any other migration. Is it possible that whoever you spoke to at Zen has also been confused by "transfer"?
Is there any reason you didn't just order online, or doesn't Zen have an online order facility for FTTP? I would expect the normal Ofcom migration rules to apply, see Ofcom GC22
Then we come to the modem. On FTTP, in effect you haven't got one. It is part of the Openreach installation and you simply connect your router to it using ethernet.
The standard migration process as referenced above does not require you to contact your existing ISP at any time. Once you trigger it they have to notify you of any outstanding costs with them, or that will be incurred by your leaving. You can cancel your migration order if you wish at this stage by telling your new ISP (Zen in this case) that you do not wish to go through with it.
If BT T & Cs require you to give a month's notice, I'd be very surprised if that is invoked under the current Ofcom migration rules. I've never heard of it being.
Having said all that, this post in your previous thread
seems to explain what actually does happen, and not what I expected. Which does tie in to some extent with what you say. I spy a hole in GC22.
Maybe a PM to him as to what you do about the existing BT connection would be worth a try? With the answer (if useful) posted to enlighten the rest of us for the next similar case
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