Ola Money — OLA postpaid calls and messages even after paying cash

I have been receiving calls and messages from OLA money regarding pending postpaid bills. I have paid the driver in cash for every trip. I do not use OLA wallet and never opt for postpaid. Now my account shows pending bills and late fee for the same. I will not pay any money when I have already paid cash for my trip. I feel like this is fraud and will not be entertaining this. the messages and calls are threatening about a legal action. I want all calls and messages to stop and my bills cleared.