Try ringing the UKFSN helpline that goes through to Entanet. I think 0333 101 0600 may be the one. They can issue a MAC - as Entanet provide the MACs to all their resellers for Entanet connections.
Cheers, managed to get mine from the UKFSN website during a rare uptime event. A colleague of mine had to go through Entanet as you suggested though, and it all worked out fine for him too. We've both since migrated.
Got to say, over the years I've read so many negative views of UKFSN and Jason on here it's unreal. Maybe I was one of the lucky ones, but every time I contacted him he responded quickly and fixed whatever my issue was fairly promptly. Maybe it was the tone and wording of my emails that made a difference, I don't know.
Whatever, I was happy to remain a customer of his until recently, when it was clearly evident that the writing was on the wall.
UKFSN was good for me. Your mileage might well have varied.
UKFSN - ISPC - Edinburgh Node