This may be confusing but I'm going to try because I REALLY need help...?

My dad had a camper on a lake here in South Carolina. It's been on a lot at a little camp place for about 4 years now. Last year he paid rent up to January. The owners/landlords don't go to the store/office during the winter so the tenants are usually expected to catch up their january, february, and march rent once they start things up for the warmer months. After not going to the lake for several months, my dad went to pay his rent the beginning of March only to discover that his camper had been moved off his lot and another had been moved in his spot, using his huge covered porch he built and payed for. When he went to the office, the owner stated he had tried to get in touch with him but didn't have his address and that he had to pay over 6 months rent to be able to get his camper, so they are basically holding it hostage for money my dad doesn't owe. A week after, my dad received a certified 'no trespassing' order, so they obviously lied about not having his address. NOW they're trying to charge a monthly 'storage fee' until he pays the nonexistant debt. THANK YOU FOR READING ALL OF THIS. ANY ADVISE IS WELCOME!