The Guidance Counselor in school mistakenly added the recommendation letter of another student (who happens to have the same first name as mine) into my Common App. It’s been locked and can no longer be taken back. I haven’t submitted my Common App yet. What is the best way to rescind or cancel the wrong recommendation sent? Or what is the best alternative? The Common App people do not respond to our calls and emails.
Did he give the other you a good recommendation? 
In this case, I’d drop a note to the individual schools, simply noting the issue…not making it too big of a deal…and then mention that you’re working with the Common App people. I’d ask each school how they’d like you to proceed.
The Common App people do eventually respond. Give them a bit of time.
One work-around - as noted above - would be to have the counselor send a letter to each individual school. The Common App also has an “Additional” report, besides the Mid-year and Final reports. The Counselor could submit the correct information there, if he or she is not planning to use that report for anything else. (Some schools use it for an additional grade report if they are on an unusual school calendar.)
How did you figure out the wrong recommendation was sent?