American Express - Complete refund was not credited back to my account

I ordered a mobile phone on amazon using american express card. I placed my order on ** Jan, ****. But some personal reason, I cancelled that order. After cancelling that, refund of that amount was not initiated on my card. My order value was ***** indian rupees. I contacted for the same with amazon and american express representatives. They asked me that due to some technical problems it's taking some time and it will we get credited back to your account shortly. On *th March, ****, American express release a letter mentioning that Amazon is agreed to refund of ***** indian rupees on your card for the same order and that refund will get initiated on your card very shortly. They initiate a refund of only **** indian rupees on *th March, ****. While it should be ***** indian rupees. I contact them more than double digit times but there response was that there were some complexities on there side and i will get my refund in next *-* weeks. That was happening again and again after every *-* weeks. They initiate a penalty charge in my monthly statements for late payment fees for not paying that amount to them. I contact them for the same then they agreed to revert back late payment charge since this was not a due payment. It is their fault not mine. I an suffering a lot because of them and not want a solution for my grievance ASAP. Now, i want to make them suffer for the same. For that i need your help in this matter.