Referral program disaster: offered free add-ons for house cleans and got zero referrals

So I tried this referral thing where if clients referred a friend for a full house clean, I'd throw in a free oven scrub or something. Used my Hoover commercial vac to demo it on a test job, thought it was genius. Ended up with a bunch of one-off jobs but nobody actually referred anyone, just kept asking for the freebies without the referral. Saw a similar flop in the Cleaning Business Owners group, guy said he wasted a whole month on it. Watched that Melissa Maker video on upselling cleans, figured referrals would be easy add-on, but nope. Now I'm back to straight quotes, no gimmicks. Anyone got a referral script that actually works for residential cleans?