Yup, bloods are done around 28wks. And Anti-D if you need it. NHS Purple book guidance.
MW should have written contact numbers on your notes, ring one of those and explain if not, then:
If not, ring GP back and ask to speak directly to the practice manager. Get them to sort (explaining this isn't the first time you've tried to sort this with the surgery and it's unacceptable that they're essentially blocking you from recieving proper antenatal care by refusing to give contact details for a MW/someone) it and say you'll give them "until the end of the day, or until tomorrow lunch time"...they're just as responsible for your antenatal care as the MW team is.
If you're near a hospital with a maternity unit, there's a good chance they have an antenatal unit, so might be worth calling them if you get no luck with MW or GP fairly promptly. You can usually get the number for these guys online somewhere.
You have the right to timely care, just like every other Mum out there. You shouldn't have to wait until Jan for an appointment, what are you meant to do in an emergency???
Difficult to be hard-ass, but I've found some receptionists at GP surgeries are often a little too jobs-worthish sometimes, to the point of risking people's health, despite NOT being medically qualified to make these decisions. Just go straight to the practice manager, refuse to tell them why until you've got to someone with medical qualifications/power that sees this is important - you have the right to not disclose this information to an unqualified person.