do you mean when caller hear system message asking to press# to return operator ?
If this is that case, then in your PBX create a fake operator extension with no voice mail enabled then go in global settings and replace real operator extension by fake one.
Now when callers will press # theys will be forwarded to fake extension without voice mail and then call is ended.
other heavy way , duplicate prompts set, then edit audio file played and remove part asking to press # to return operator, then set your prompt set to be used instead of default one.
none of these two workaround is a good solution but first one is easy to set or remove.