If you have Chiari malformation you need a base of skull MRI. We regularly see these as symptomless incidental findings they are noted only. I am somewhat surprised you have not been sent for MRI of that area already given your diagnosis however there really is a postcode lottery in NHS. As Pas says contact your consultant and request an urgent appointment. You can also record your consultation so you can re-listen to make sure you have not missed anything as it is very easy to forget parts of a conversation when one is stressed/worried/in pain.
I had to pay for my own lumbar MRI and went to Cobalt in Cheltenham, I cannot even be referred to either a Neuro-surgeon or Othopaedic surgeon as local policy is that a person has to develop acute Cauda Equina syndrome BEFORE they can have a NHS MRI and that if necessary a decompression would then be done. The reason I have had the MRI is that if I get acute compression signs `I will attend A&E clutching the MRI on disc and the Radiologists report. I have already had 2 discs removed as an emergency from my cervical spine!!!