Property Boundary Fence Went Over Our Property

[Jason2222]

My question involves real estate located in the State of: Oakland, CA

I bought my house a year ago, and the fence of dividing my neighbor's property and my property began to collapse/ fall over to our side because the properties are located on the hill. While my neighbor's property is on the upper side of the hill and my property is on the lower side of the hill, the fence dividing the properties is gradually falling over to my side. It has already tilted more than 2 feet on a 8 ft fence. We asked the neighbor if we can fix the fence together and share the cost equally, but they decided that it is my problem and they won't pay to fix it because it cost over $10,000 to fix this encroachment problem. Is there anything I can do to make my neighbors pay to fix the dividing fence?

Any help would be appreciated. Thanks