This seems odd. What happened when you called them and who did you call? Didn't they say they would consider it and revert to you by phone or offer to negotiate?
You need to call them again, or call in and make an appointment to see the manager and ask them to fully explain why they are doing this. You also need to set out your circumstances, including a detailed budget, explaining why you are requesting this reduction in payments, and why it's neccessary. If you are anxious, write out all the questions you need answers to in advance. Also ask the bank who you can appeal to, and perhaps ring MAB's to know your rights.