Fence company refusing to move our fence that they installed onto our neighbors property.

Location: Indiana

So basically a few months ago, we had a fence company build a fence at our new build home. They used a plot plan to determine where the fence would be built. On one side we are well onto our property due to a utility easement, but on the other side, we built the fence out to our property line. A few weeks ago our neighbor decided to build a fence and when their fence company came out to measure for their installation, we realized that our fence was installed between three and six inches (it angles out to the back corner)onto their property.

The fence company is claiming that they don’t make any changes if the error is under 6 inches and that we approved the plot plan. The back line of the fence should be 67.5 ft and it is almost 68ft. We did approve the plot plan but the fence they built is not what was on the plot plan. There is nowhere in their terms and conditions that mention this 6 inch rule that they keep claiming. What should we do?