That's terrible. I can understand why it's frustrating. Hell I would be thru the roof and go to whatever office I could get to and... probably get arrested for harassment, because I can generally express my anger with more volume than people are accustomed to, plus I can be very articulate when I'm pissed. Not trying to give you any ideas, ofc.
Short of that, is there any possible escalation path? I am ofc ignorant of how the NHS functions, but I'm guessing there might be an office that you could approach to escalate your concerns re: your treatment being inadequate. Of course, they probably have a 5-week response time, anyway. I know what black market meds are (as in completely illegal), but I don't know what grey market is - is that like ordering from a foreign country without needing a prescription? But if it worked, and you know the seller is reputable, then why not?