Change in due date for payment - No response from call center supervisor

MTN has migrated to a new billing system and have unilaterally changed due date for payments from 25th to 17th. I called 3 times on Monday with queries but the "customer service agents" all working from home and are unable to transfer my call to a supervisor/manager. Despite being promised that an email would be sent to a supervisor/manager to contact me urgently, I have received no feedback. Very frustrated.