A 32-year-old man from rural India presents with a 6-month history of foul-smelling otorrhea from the left ear following a suppurative ear infection in childhood. On otoscopy, there is a marginal perforation with granulation tissue and a whitish mass visible in the external auditory canal. Pure tone audiometry shows a conductive hearing loss with an air-bone gap of 35 dB. High-resolution CT temporal bone reveals erosion of the scutum and malleus with soft tissue density in the attic region. What is the most likely diagnosis?