Nimbuspost Private Limited - Courier Integrator Company NimbusPost Fraud

I am using Nimbuspost Courier Integrator to ship my products to customers. Now they have started doing fraud in the way that they will show on their panel that customer refused to accept package and they made two attempts but all fake. They have done twice with me in this way even my customer told me that he was waiting for the product to be delivered. When I approached nimbuspost customer support they asked for proof. I provided them all proofs - call recording, whatsapp chat sscreen shots but they keep denying the proof and when i asked that please provide me courier person call recording with customer then they will not provide any reply and close the escalation. Twice they have not rdelivered the product and nor returned product back. They might be doing such fraud with so many people and making money from courier charges and also selling product of their own. We need to stop them for making fraud and cheating customers any further.