I assigned 3 swordsmen to a Draugr.
Draugr has 1 health and 1 hit
2 blank 1 shield
shield was already used so I have 2 dice now
1 blank 1 shield
shield was used I have 1 die
Is this correct? I didn't lose a single die but didn't do damage as well, but lost the combat right?
No sir. I don't believe you lose a shield for using it. If your target survives the round of combat and you have warrior dice left over (not lost to damage) you begin a new round of combat against that target, rolling all dice that have not been lost. That's my interpretation of the rule Details of Combat 5b.