A number change wont always cease the adsl, more change with a name change, but thats more if it's a billing name change (rather than changing it from fred to joe) A cease on the phone line WILL cease off the ADSL even if you could get BT to do a cease and re-provide, but that will start to get messy.
It could be an option to keep going back to ofcom and tell them you have tried everything, make sure you have a note that you contacted them (however many times) and that you also spoke with the upstream supplier, who refered you back to HV and you now stuck in a loop. You never know you may get someone who wants something to do, and will follow it up by getting in touch with the upstream provider and getting them to generate the MAC for you.