Tonight our opps bid to 6s, going down 2. My lho (after I had opened the bidding with my 17-count) at his first turn bids 7NT, then leaves. I called director, she subbed for the 7NT bidder, then asked me if I wanted to accept an Undo. I was completely unaware that I actually had that option. I told td I wanted actual result, which would have been 7NTx -4 or -5. I was told by the TD I was 'childish' for not accepting the undo, forcing the sub to sustain an awful score. When the scores came up after the round, I saw we were given an adjustment of -3, which completely shocked me. We were being punished, even though the opp was the guilty party. I was told that if I didn't like the ruling then please don't play there any more. There is a specific rule that says "NO UNDOs", so I didn't know I could accept it. What gives?