on "Add on code 29826 denial"

Hi,
I need help on this one. I received a denial on 29826 59.
Procedures performed: 1. Left shoulder arthroscopy with subacromial decompression. 2. Acriomioplasty. 3. Bicepts tenotomy. 4. Rotator cuff repair, mini open. 5. Distal clavicle excision, open.
Payor is telling me 29826 is an add on code to another procedure.
This is how I billed:
23412 Lt
23405 59
23120 59
29826 59