Definitely talk to a lawyer, one who knows about startups.
NOTE: the lawyers for your startups represent the company, so don't talk to them - find your own lawyer.
Other than that, AFAIK what you mention is not typical. Option pool should not be created by "taking" options from employees, but rather by issuing new shares which dilutes everyone equally. You should bring it up and ask that they create the option pool by issuing new shares which will at least indicate to them that you know what you're talking about and perhaps reduce their inclination to screw you.
Also, what was your vesting schedule? If it was four years, you should have already vested 3.75%, which you can exercise anytime. If they take 4% of the remaining, you're left with just 2.25% to vest over next 2.5 years, which is just wrong.
Also: before you begin negotiation, do understand your BATNA - Best alternate to a negotiated agreement. In other words, what will you do/can do if there is no mutual agreement. This will tell you if you're overall in a strong position or weak. This will include any advice you get from the lawyers, your employee agreement, etc.