Can a plumber cancel a permit after it's been passed by the (MN) city

[Federico Gutierrez]

To make a long story short.

I'm having pay dispute with a plumbing company who I hired to fix a broken sewerage line that had snapped just before the clean out under my basement. It was part of a condition on the closing side for the buyer (I'm the seller). They fixed it (I paid for their services at this point) but the buyer ran a camera prior to closing. Found the sewerage line was connected and fixed but there was not enough pitch from the main stack to the clean out line so water was just sitting there. Had to call the plumbing company to come back out, this was after I had filled the hole and cemented the holes. So owner says he would cut me a deal.... he discounted me $500 and charge me $1500 on top of the $1000 I already paid him. 

The plumber is now charging me again and I really refuse to pay for their mistake. The way I see it these guys didn't do their job right the first time, Im not the professional here but the master plumber had mentioned the pitch may have been an issue as the house had settled over the years, which in turn it was. Not only that I had to spend more time and money with filling the holes and cementing them back up to have it all ready for final closing. Sure I did this but if I were to hire a professional I would have had to pay them.

His saying that if I don't pay he will call the city of Minneapolis and have the city cancel the permit and then the buyer of the house will have an issue. Which will some how come back to me, sure of it. The house has been sold to the buyer and all permits are closed. Any advice on where to go from here?