Hi Aygun Aliyeva,
I have not come on disabling Apis for cognitive services yet. To stop using any service completely, we need to delete the cognitive service. In case of OpenAI, we can delete the model deployment from deployment tab.
You can get details cost analysis of each model deployment from Cost analysis tab of your OpenAI resource by filtering with meter of your respective deployment (with add filter options)
Attached below screenshot for reference.
To avoid high cost, you can set up budget alert and anomaly alerts with threshold cost, post which you can get notifications. Attached reference on budget alerts , cost analysis and unexpected cost handling
Thank you.