Our Zestimate is way off compare to the almost same houses on the same street

My home listed @8 George Rd, Emerson, NJ. I think the Zestimate of 315K is way off, even from the common sense.We added a level on 2001 and doubled the size. Even compared with original 1-level ranches, such as the ones left and behind us, the price is much low, not mention our lot is bigger. Just comparing with the almost exactly houses on the same street with 2 floors, same number of rooms and square feet, etc. , I did not see any reason the price is so different.Just compare to the one two houses next to us, 20 George Road, which is 7-8 years old than ours (update year), same as 4 bedrooms, 3 bath, 2500 square feet, their estimate is 506K. Our lot is 8970 whch bigger than their 8006. And we basically pay the SAME amount property tax based on the  almost same town appraisal value. You can further compare with other houses on the same street with 2 floors and same setup. I just cannot see any reason for our house with zestiamate of 315K. The reason I ask this fair question is that we are trying to adjust our home equity line. Unfortunate the local bank agency seems using the reference from Zillow. Please help to correct this error. Thanks,