water problem

We purchased a new class c mh Forest River Sunseeker, 25 ft. 2017. at the time of purchase, I received a 25 ft. water hose. We used this hose 6 or 7 times with no problems. After several times, I realized that I was close to water. So, I purchased a 10 foot hose. My problem is, every time I connect the short hose to the city water port, it fills my fresh water tank over night. Seems crazy but it does happen and the service folks can not fix it. Anyone ever heard of this?????