According to emails received and my services summary the regrade to paygo 3 was done almost immediately after my request.
Congrats to Metronet on speedy action (although another email from Metronet told me they cannot expedite it! Confusing. Hope it's really taken effect).
It seems that Metronet confused my request to change to paygo 3 with a request to uprade to 8MB/s max (already done last month), hence their statement that will take 5-7 days, and their reply to my email telling me that they can't do my regrade any quicker (in fact they put me on paygo 3 immediately so they have no more outstanding tasks to perform for me).