Best thing to do, fam... either reply to someones open battle or set up a battle prior to sending the bars. Some don't reply to random battles sent to them.
You can find them in your Battles list. Hover over the 'My LB' icon, then from the drop down menu, click 'My Battles' and you'll find them in there, fam. They won't be deleted unless you send them to a member of Staff for deletion.