Postpe — Post pe collection agent said extra charges will be waive but its not waived

Hi
Due to loss of job I was not paid postpe amount on time therefore my due become 5000 apex i recieved call from collection agent. After i insisted for some waiver on Charges she said pay 4000 in app and and other 1000 will be waived off but it's not done. I mailed to help mail id to post pe but customer service person said that show me mail proof of waiver.
How can I show this because she said pay 4000 and automatically other amount will be waived off. Also she said send me screenshot. I have sent her.
My concern is that I want my charges waiver because that collection agent said me that she is calling behalf of postpe. So post pe is willing to waive extra charges as she said.
I want to say one thing while for another payments app like Paytm, flex salary they have clear amount of extra charges as they said. But post pe want mail proof.
Postpe playing with trust first say pay amount extra charges will waiver and after payment they say can't waive pay remaining amount.
Don't trust in post pe ever Everyone l.