Good day, v-kumar.
You may have set up recurring bills in QuickBooks Online. To prevent this, you can either delete the recurring transaction or edit the template to Unscheduled or Reminder type from the recurring list.
To know more about this feature, check out the following: Create recurring transactions in QuickBooks Online. This will provide you additional resources on how recurring transactions works in QuickBooks Online.
Feel free to drop me a reply below if you need more help regarding bills in QuickBooks Online. I'd be more than willing to lend you a hand.