HCPCS Code L8699. L8699 is a valid 2019 HCPCS code for Prosthetic implant, not otherwise specified or just “Prosthetic implant nos” for short, used in Lump sum purchase of DME, prosthetics, orthotics.
HCPCS Code C1713. C1713 is a valid 2019 HCPCS code for Anchor/screw for opposing bone-to-bone or soft tissue-to-bone (implantable) or just “Anchor/screw bn/bn,tis/bn” for short, used in Other medical items or services.
HCPCS Code C1821. C1821 is a valid 2019 HCPCS code for Interspinous process distraction device (implantable) or just “Interspinous implant” for short, used in Other medical items or services.
You should be using the one that most accurately describes the equipment. If the C1821 is still considered investigational by BCBS of NC and the plan doesn't cover investigational devices then there's not much you can do. But if one of the other codes is accurate then you could use one of them. Why is the charge master saying you cannot use them?