Played my first 40K game in over 20 years…

…and I got owned by the Custodes. I bought the Custodes combat patrol and a Black Templars Combat Patrol. Played with a friend - I was Black Templars. Not really a fair fight (we played a simplified version of the regular rules, not a combat patrol game and Custodes had a points advantage), but my god the Custodes pack a punch. 2 Allarus Custodes + captain single-handedly took down my 10-man Crusader squad and only suffered 1 casualty. Toughness 7 and 2+ SV is no joke. My Templars had plenty of opps to attack and got into melee but it kept feeling like I brought a plastic spoon to a sword fight. Impulsor barely made a dent in Warden unit too.

Any thoughts on how to fight Custodes with a Templar army?