Talk to Ent Specialist on Ear Infection

My father had an ear infection for past 8 to 10 years.He took medicines prescribed by Dr zafar iqbal. Last year he had modified radical mastoidectomy done. After surgery his ct scan report was fine with no residual mass lesion but there was still slight discharge which increased with time. The culture report showed heavy growth of pseudomonas aeruginosa. He did course of gentamycin as prescribed but the ear is still not dry and the hearing is almost gone in that ear. Can anyone tell what our options can be to dry the ear and improve hearing? He is 57 years old and diabetic for 20 years