Hello Sag
I experienced similar probs with my mum. Having written to the surgery several times, the doctor eventually called me, but could not discuss mum's case, per se, because of patient confidentiality (which I understand). I felt aggrieved because I'd had to write so many letters. Eventually, I went with mum to see the doctor about one thing and I'd primed him to drop into the conversation about her memory. It worked and he referred her. However, up to that point she (and the various doctors I saw) batted my concerns away with the usual cr*p excuses.
As Katie said, you must tell lies in order to help your mum. Is she on any medication? Perhaps you can say the doctor wants to check this and they are doing 'general health checks' or some such story. Persevere! I found this part to be the most difficult, but once the consultant became involved, things did start moving. In any case, as I've mentioned to a new poster on here today, it might not be dementia, so to be sure, the doctor should rule other things out.
I hope you get something sorted. You have done the right thing.