Ask your broker why. While option holders are not entitled to any dividends, all strike prices need to adjust by $5 to prevent those from profiting "unfairly". If it was that easy, people would load up on the $155 puts yesterday to make a $5 profit today. If your broker will not adjust or gives you a lame excuse, then contact the OCC (Option Clearing Corp) for help. You've got a strong case. You should not be losing $4 unless COST goes down drastically tomorrow.
The special dividend doesn't affect the price of the option. Your strike just gets moved down by 5 strikes. So if you originally purchased the $152.5 call, your revised call will now be the $147.50 strike. If COST closes above $147.50, you will be put the stock and the value of the call will be the worth the price of the stock minus the strike price of $147.50. If COST closes below $147.50 tomorrow, yes, the call will expire worthless.