API credit exceeded error even though didn't used them

I am getting You've reached your usage limit. See your [usage dashboard](https://platform.openai.com/account/usage) and [billing settings](https://platform.openai.com/account/billing) for more details. If you have further questions, please contact us through our help center at help.openai.com. error even though I’m using the API after about half year and my credits are not refilling