not to judge but you left them hanging by not signing it within 3 days without any communication doesn't look good. Anyhow that's water under the bridge, what you can do know is have the hard talk with HR and see where it ends which would be the best.

The next thing is not recommended, burn the bridge & village and move on to Comp B. Comp A may or may not take legal action, and as you said its a normal lvl position vs the legal resources + effort it usually takes in these matters they may well just let it pass, BUT for one you will have that record following you.

So take your pick on which route you feel is the right one.