A 58-year-old woman from Mumbai presents with a 3-month history of progressive pain and swelling in the left submandibular region. On examination, the mass is hard, fixed to surrounding tissues, and the overlying skin appears erythematous. She reports difficulty in swallowing and a recent episode of facial nerve weakness on the left side. FNAC reveals mucous cells, intermediate cells, and epidermoid cells with marked nuclear atypia and increased mitotic figures. What is the most likely diagnosis?