How to get a refund on wrong charge of prepaid service?

Hi, 

I recently transferred my number to other carrier.

But T-Mobile prepaid service charged monthly payment through Auto-pay service.

I thought it would be automatically stopped but it charged.

I requested a refund to the representatives at the call center and they confirmed that I did not use any data so that I could receive it within 10 business days. So I just waited. 

But I have checked other representatives and they insisted that I used the lines data and even the line was alive. 

It is impossible because I have records of using data from other carrier.

What was going on there? The incompletion of port-out process is the mistake of T-Mobile technical team but do I have to pay for the monthly payment which I did not use at all?

I want to receive my money back as soon as possible.

I sent the mail to the customer relations team with the evidence of my usage of data on other carrier, so please solve this problem and send my money back as soon as possible.