After modified radical mastoidectomy or radical mastoidectomy its normal to have some hearing loss as intention of this surgery is complete removal disease and hearing improvement is a secondary concern. You need to under go audiogram. If your hearing loss is conductive type then revision surgery can improve your hearing significantly. Only other option would be use of hearing aids. Calculation of disability requires a audiogram and You need to consult a govt certified ENT specialist for such an certificate and which can be used to avail benefits if you are eligible