Outrageously rude mtn agent

My mother and father made a call to query about mtn router 14/01/2025. The agent insulted my dad who is 68 mind you and then went off at my mother who is 65 . I'm do angry and hurt and we took down her name and she told my parents there's nothing they can do to her. Please help me find a place of seeking justice my parents get lots of money deducted every month end by mtn