Sound like Sky's systems needed updating (and hopefully have by now). As Matt says, Sky physically take over the line when you take their broadband, and MACs are only applicable on BT Wholesale voice lines.

In reply to a post by jchamier:

Makes sense. Two complete guesses then, it was raised as two jobs, rather than a migration. Or the losing ISP is trying to claw back some money.

Yeah, perhaps Vivaciti's systems raise a cease charge when an MPF migration is underway, even though Openreach doesn't ultimately bill them. A nice earner!

Cease Fee by Vivaciti in ISP Unhappiness Feb 12

This is not the first time an issue has been made about cease fees and Vivaciti. Whether or not and who should pay has to be talked about . However it was the subseqhent action by vivaciti that was concerning.
To be honest, i would request proof of Cease Line implementation from Vivaciti and pay bill.
Advise Sky that as they have forced payment by ceasing line, either they pay or you will request Ofcom judgement.

In reply to a post by flippery:

request Ofcom judgement.

Although Ofcom wouldn't get involved... It would be a ADR issue.

Matt