Question Sequencing of Codes for Administration of Chemo, Immuno or Radiotherapy

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Coding rules state that if a patient is seen for the administration of chemo, immuno or radiotherapy we are to sequence the appropriate Z code (encounter for) primary and the malignancy codes are secondary. We are having a lot of commercial insurances deny for high dollar drugs, and the insurance company is stating that we need to re-sequence the codes to make the malignancy codes primary and the Z code for the encounter secondary. I have never experienced this before, and that violates the coding rules and regulations. Our billers as well as our CDI have asked me to change the sequence of these codes so insurance will pay. I have never been in this situation before, so I am unsure what information is accurate.

Can insurance companies request codes to be changed around to not meet the coding rules an regulations and we as coders are to do this?
Do payer rules trump coding rules and regulations?
Has anyone else experienced this, and if so, how do you handle the situation?

I am not comfortable just changing codes around because someone tells me to, however, if there is a validity to this and I should be doing what the insurance companies are requesting then I want to do so. I am just trying to find some reliable and accurate information to handle this situation and what is accurate and correct as far as coding goes.

Any information or advice would be greatly appreciated!!