Money owed

If someone purchased something for me but haven’t given me the price (I asked twice)
Am I liable to keep asking them?
What is the proper course of action?

Not sure what the issue is.

my sister purchased groceries for me and did not tell me the cost. I asked her a couple times and she never got back to me.
Is it my job to keep asking her what it cost or do I wait until she decides to give me the price?

Thank you

I am a bit confused as to the specifics of your questions.