I was fortunate enough to have been laid off on December 31, at which time I received my final paycheck and a payout of my vacation and personal day balance. Upon reviewing the pay stub for my vacation balance I noticed that Verizon had deducted an additional installment for my 2015 healthcare savings which put my deductions beyond the limit. For example: there were 27 pay periods in 2015, so had you planned on deducting $20 per check the HCSA available to you in 2015 was $540. However, if you had a vacation payout at the end of the year Verizon ended up deducting $560, with the additional payment going to the administrator i.e. not available to you. It's easy enough to verify - just look at the YTD total on your last paycheck and your vacation payout.
Don't bother contacting HR or Payroll, you have to contact Benefits Connection (855-489-2367) in order to get this reversed. I know of at least 4 other employees here in California to which this happened, and I can't imagine we're the only ones.