He filled up my junction boxes with drywall mud!

Over the years I found several old, hidden junction boxes filled with drywall mud. The flipper did that. So the last thing I would expect from my drywall contractor is to fill up my new junction boxes with drywall mud! My new wiring is encased in dried mud! I am so tired of sloppy contractors! I’m furious and I let him know it. I demand that he clears and cleans every box back to pristine condition.