Call your hospital (not doctor) ask to be put through to the outpatients ct department and ask them if they have received the referral.  If by Friday they haven't, then call your GP back and tell them the CT department doesn't have the referral.  Then call the CT department back on Monday and ask them if they have the referral and then when they say yes, tell them that you want to be put on the cancellation list and that you will come for your CT Scan at anytime on any day, that they just need to phone you, this should get you a CT Scan within a month.  Instead of 4 months.