Possible overcharge on our account

We had gap between amount charged on our account and actual usage on our API usage report, and it seems that credit has been disappeared from our account.
We would like to clarify the facts on this issue as soon as possible. We would like to use perplexity API however, we can not proceed to recharge unless we understand billing logic correctly. I have been often contacting support@perplexity.ai for 3 months but received no response yet. Wishing your support here. Thank you!