Need advice - Land survey issue

My dad inherited some agricultural land in suburbs located near water course government land from his grandfather. He surveyed the land using govt surveyor back in 2010 and built a house and fenced the property. He also passed away recently. Since the fencing was old and damaged we planned to resurvey the land. The new government surveyor surveyed the land and said that your land measurements were wrong and your actual land was behind the house. And our 75% of our house was in government watercourse land. We have no intention of building the house in watercourse land . Im so afraid of eviction now, since my house is in government land what to do. Im also willing to give up my own land, but not sure whether they will be okay with it. Kindly let me know of my options now Im planning to do private survey too please help me sort this issue