If my doctor has provided my insurer with documents stating that it is necessary tI have a diabetic pod to sustain life, can it refuse coverage?
Yes, it may refuse coverage if:
1) your policy does not cover devices/procedures like that;
2) if the diabetic pod is considered "experimental" treatment (I don't know anything about diabetes, so I have no idea if this would be the case)
3) if it believes that you don't actually need it--the insurer is not required to take anything a doctor prescribes at face value, if, for example, it has reason to believe the procedure is not actually necessary
However, you do not have to take the insurer's determination at face value, either: if you feel the insurer is not paying for something which it should, under the terms of your coverage, you could sue it to try to force it to pay, and a court/judge will determine if this device/procedure is covered in your case.