CPT® 64455

We have billed a CPT® 64455 while there is a CPT® 20550 along with Modifier 59. The provider is a Podiatrist. The payer (Golden Rule) has processed and paid CPT® 20550 and applied the allowed amount towards patient's deductible, however CPT® 64455 has been denied stating CPT® 64455 cannot be billed as unbundled. Any suggestions and directions would help. Thanks,
Neo