Pay twice for the water supply device?

Hello, Before I come to my question, I will briefly explain the situation. My father-in-law had a plot of land in Bischofsgrün. This plot was undeveloped. He had a caravan permanently parked there with a fixed awning and had registered water and wastewater. The caravan was connected to the water supply and electricity. In 1984, he paid water and sewer connection fees. Unfortunately, he passed away in 2016 and left the plot to my husband. Since we wanted a bit more luxury, we bought a mobile home and set it up there. For that, a building permit was required, so it counts as a building. The plot is now developed. Now the municipality sent a bill for the installation of the water supply and drainage system. When I inquired, I was told that if a house is built, you have to pay for it. Wasn't this already paid by my father-in-law? Do I have to pay it again now? I would appreciate helpful answers.