“Jingle Bell Heist” is an over-plotted, under-charmed rom-com about robbing from the thieving, unaccountable rich and giving to the under-insured.

In soft drink terms, it’s a Diet Coke that’s gone flat — familiar, not particularly surprising or the least bit fizzy or satisfying.

Olivia Holt of “Heart Eyes” and TV’s “Cloak & Dagger” stars as an American living abroad with her English mum, picking pockets and pilfering her posh department store in a sort of rough justice against the insufferably rich.

Cell-phone-fixer and tech “security” wannabe Nick (Connor Swindells of TV’s “Sex Education”) is the Brit who spies Sophia on the Sterling’s store security cameras lining her pockets and occasionally punishing rude customers with her light fingers.

But Nick isn’t supposed to see that. He’s hacked his way in. He’s got a heist planned. Sophia may be coerced into joining him.

He’s got a grudge against the irredeemable “a–hole” who owns the place (Peter Serafinowicz). And she’s got a sick mum who needs a pricey experimental treatment to save her life, and doesn’t have time to wait for the National Health Service to get around to treating her.

But but “We moved back here for the free health care!”

Our mutually-mistrusting thieves consider one scheme, and then another and then a third when the first and second are complicated by the shady business practices of the Sterlings (Lucy Punch plays the libidinous Mrs.).

Attempts at “suspense” in the heist itself are ineptly handled.

The script and the leads strain to wring the “cute” out of this, but that’s in short supply.

I’d quote a funny line or two except there aren’t any. The capers involve attempted seductions — stage managed via microphone and earpiece — that fall flat.

Punch, one of Britain’s funniest, has nothing to play and Serafinowicz (“Guardians of the Galaxy”) has too few scenes to ma\ke his cruel cad funny.

Perhaps there’s entertainment value in swooning over our attractive leads or the assorted needle-drops that make up the score (Tchaikovsky’s Violin Concert in D has a certain action/comedy kick here).

But come on. Dressing a bad caper comedy in Santa suits doesn’t solve anything.

Rating: TV-PG

Cast: Olivia Holt, Connor Swindells, Peter Serafinowicz and Judy Punch.

Credits: Directed by Michael Fimognari, scripted by Abby McDonald and Amy Reed. A Netflix release.

Running time: 1:36