Cred — My amount was not credited to card on time

I have made a payment using cred app. First, it displayed as successful. But later it displayed as failed. And the amount was not credited back until a week. Due to this, the fine was charged on my credit card stating late payment. And now when I have approached the cred for a refund, they are delaying saying that they are working on it for a month. In the first call, they said they will refund. But now they are not responding. It is not at all my fault to bear a 30k fine. I need my refund back as it is not my fault. Please do the needful.