My question involves real estate located in the State of: California

My Mother bought this house in 1987. Before the purchase of the house, it was in probate for a year or more before the house was up for sale. The house had been vacant during the probate period. We started working on the the house (the garage area) and realized that we have "NO" access of getting on one side of the garage, from the front or the back side of the garage. The yard fencing runs and attaches right on to the back side wall of the garage !! But the top roof of the garage exceeds over 6" over the fence line.

So what I'm getting at is that the neighbor moved the fencing to gain more property
and moved the fencing (probably during the probate year). Also note that the neighbor uses the side of our garage for his ladders, and other garden tools, etc...we have "NO" access to the side of "Our" garage ! The garage is our property. But he has full use of it and we don't !. He fenced and closed the access off so even if we want to fix, paint the side of the garage...we have to go over to his house and ask to access the side of the garage. Does that seem correct ?

What would be the right procedure in dealing with this neighbor ? And most of all...what are the legal rights for "US" if the neighbor did move the fencing while the house was in probate ? The fence which stands from the entry of the driveway to the garage...the neighbor also built the fencing himself. Would the neighbor have had to get a city permit to build or rebuild the fencing (which we highly believe now is on our property). All done while this house was in probate...the property boundary
line was moved. There is "NO" way that a garage would be built exceeding the property line into the neighbors. It's seems that common sense tells you that it would be against the building code.

Need help as this is quite new for us. What would be our first step ? Thanks