Did you try emailing support? My Bro-n-law used some of his real name for his original username (i.e. his name John Smith - username jsmith9999), so he called support and mentioned that our boss(es) play on BD and that he was skeered one of them might see his username and put 2&2 together and asked if he could change his name. They stated they normally do not allow it except in extreme situation, but they would allow it this time.
It's always worth contacting support 1st.
My suggestion now, contact support, let them know what you've done. Explain you did not realize it was against the rules to have a second account and to please close the original account if at all possible. If you're open and honest they will probably work with you.