Sean Allison bad service, doesn’t pay back on his incorrect invoices

Hi guys, I used a plumber by the name of Sean Allison, he did the job, but made me pay him before he left my complex. He overcharged me and I now find myself constantly asking for the money he promised to pay me back. It has now been 7 weeks. I will never get this money back! Never trust a plumber who makes you pay before they leave or before you can check the invoice!