New job not accepting my qualification

[Greenhouseparrots]

I recently had an interview, got the job and then heard nothing for a month. I tried contacting them for a week and heard nothing back and eventually got through to someone who told me my qualification isn't recognised and they can't offer me the job because of it. My qualification is definitely recognised and I've got a second and third opinion as well as double checking myself. I know where the person checking it has gone wrong but I can't get through to anyone to explain it to them. They keep saying they'll call me back but no-one is. I turned down another job for this role and I'm now out of work because I've left my old job due to getting this one. The person dealing with my paperwork is apparently on holiday so that's why no-one has contacted me sooner, but now no-one is able to talk to me at all and they keep saying they'll call me back but don't. I'm definitely qualified, have great references, experience and the sector I'm in needs people with the qualification I have so there's no reason for me not to have this job other than someone made a mistake and now I potentially don't have a job.

I don't know what to do. The setting itself is fine and understands but their compliance department are the ones that made the mistake and are saying I can't work there as I'm not qualified yet I am. Sorry for venting on this forum, I'm just waiting for them to call back and wondering whether I should be job hunting instead.