my firm headquarters are in NYC and i am a NYC resident;
but i worked in the company premises in NewJersey for a period of 2 months.

the company withheld taxes and paid them fully to NJ state.

however TODAY they told me that was wrong and all taxes should be paid to NYC.
this "error" is still present on my current W-2 form.

Since they were wrong the first time, based on the information provided are they right
this time???

Based on their opinion, now i can claim back in full the taxes withheld
from me and paid to NJ while on the other hand i need to pay in full the state taxes in NewYork.
I am a non-resident in NJ, so I am using the NJ-1040NR form. but how do I claim back the full New Jersey amount?

Am I doing it correctly if I put ZERO in line 14, column B (wages from NJ sources) and proceed from there onwards?

IMHO, since you worked within the confines of the state of NJ, you ARE liable for NJ income taxes for that period of time.

File as a non-resident of NJ and declare only the income earned while in NJ. Then claim a credit for the NJ taxs paid on the NY tax return. If you file paper returns, attach copies of the other state tax returns when you mail in the state tax returns.

The resulting credit should probably be dollar-for-dollar, so you will lose nothing tax-wise and you WILL be in compliance with the law.

Any competent tax preparer in your area will know how handle this. If you want, I can do the return (assuming you have not already filed).

PM me if you are interested.