app developer

I am a milkman. And I serve milk door to door. The thing is when it’s month end and I make bills for them but some or many of the customer’s told me that your bill is wrong. But from my side it is correct. So I need an app where I(admin) can entry of the milk and the customer’s (user) can able to see them(only read operation not update or delete)
And I want to buy my milk with online delivery.