It is still best to ask for a MAC, even if Sky do not require it. Also check the BT Terms & Conditions to see whether the issue of a MAC starts your notice period, whatever that is.
When requesting a MAC, do not mention the words "Cancel" or "Cease", as these may be taken literally and a
Broadband Cease order put on your line
by BT. That would screw you up. If you can request it online that is safest. If by telephone say you are intending to migrate it, and I always refuse to say which ISP I am moving to - you have no obligation to tell them.
The reason I recommend asking for a MAC is that it shows you are complying with the Openreach migration system. Some people migrating to full LLU as you will be doing find they later receive a charge of around £29.99 from the old ISP, for the
Broadband Cease that is part of the move and is triggered by the LLU provider's order. You/they should not be charged this, but having requesting and received a MAC is useful evidence in your favour if you do.
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My broadband basic info/help site - www.robertos.me.uk
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Internet connection - Plusnet Value Fibre.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.