Chasing collections on a $6k LVP install job - customer ghosting me

Been chasing this customer for weeks now on a $6k luxury vinyl plank install we did in their kitchen and living room, and they're straight up ghosting my calls. I'm up in Minnesota and the subfloor prep alone took us two full days with that Ridgid moisture meter showing levels all over the place. Sent the invoice through Housecall Pro right after demo and install, but now it's 45 days out and nothing. Guy in the Flooring Contractors Network group said to file a mechanics lien ASAP, but I'm worried it'll kill any referral potential. Anyone else dealing with this crap on flooring jobs? Saw a similar rant on r/Flooring about a tile guy getting stiffed. What's your go-to for collections without turning into the bad guy?