Bad service-FNB COLLECTION DEPT

I am trying to inform FNB that I can no more afford the credit card repayment arrangement of R5400 that I have since being paying for the past 3 years now..and their collection department is taking me from pillar to post When I inform them that for now I am only able to afford the R1500 until my financial situation improves They tell me that it’s not possible…I don’t know what to do anymore Should I stop paying them and get black listed or should I just pay what I can afford for now?

My other request to them was that,I CAN CONTINUE PAYING FOR the next 2 years to make it 5years in total and then they should cancel the Interest on the debt,since I have never skipped any payment and to date I paid the total of over 180k Please assist