Fentanyl conversion is not a atraight conversion from one opiate to another. Because the delivery systems are very different- oral versus transdermal.
It is very likely the conversion dosage rate is fine- however since you are going from oral meds to transdermal - it needs to build up in the bloodstream and the tissues so that you are receiving a steady dose. This occurs over the first two or three patch changes and the breakthrough during conversion is usually handled by allowing a small dose of oral meds (5 mg or so of old med) during the first week while changing opiates/delivery system.
There is likely some info I don't have, but it is abundantly clear that EVERYONE responds to pain meds individually. There is no exact conversion ratio among opiate pain meds that fits everyone. First and obvious is to go back to what worked. Then, if you have a real need to change to fent, titrate slowly down w oxycodone and up w fent.
Second is to understand why the decision to switch. Fentanyl patches are great for some people. Not for everyone.
Insurance is another question. They're just being the cold blooded, money grubbing scum both insurance and Pharma always are while bulking you out of $$$. Keep after them for coverage and for fair price.