Physical therapy first is always a prerequisite on w/c cases. As others have stated, if they are denying the mri, get you a lawyer now!
You are probably dealing with Liberty Mutual. They will do anything and everything to try and get out of the claim. Trust me... been through it all with them. They will lie to your face all the while doing the complete opposite. I really had a hard time believing it was true until I caught them in so many lies. My doctors were telling them I needed surgery and they still tried denying it. I sat at home over 6 months on two different surgeries waiting for them to approve
treatment. Wish I had gotten a lawyer sooner.
Once you get a lawyer and they see you are serious, things will change.