Since you did not receive the amount of income reported on your 1099-B in 2017, you may need to have your company issue you a corrected 1099-B for the actual amount of income received for this installment sale.
According to IRS publication 537, Page 2, You cannot use the Installment method to report gain on the sale of stocks and securities traded on an established securities market.
https://www.irs.gov/pub/irs-pdf/p537.pdf
I understand the agreement with your company, however, the 1099-B is the record to the IRS of the actual amount of money you received in each year for the sale of the stock.
