I was talking with a Japanese girl by message and she asked me how to read my name, which is Andrea (Spanish female name). I told her it's アンドレア but that some friends call me あんちゃん because it's shorter.
Her answer was: あんちゃんおん
I didn't understand the meaning of this おん and after searching in dictionaries and so on I have no clue of how to interpret this as something you would add to a name.
Thank you in advance.