You will have to contact Pakistani embassy to find out the steps you need to take to renounce your Pakistani nationality since its not automatic.

Why don't you argue it with the authorities to let you keep both ? Giving up your Pakistani nationality is rather abnormal I must say.

 

The law on this one is actually ambigous. It says you are not REQUIRED to give up your current nationality but you MIGHT be asked to do so and thats what has happened in your case. So while the voivodship are within in the law to ask you to give up Pakistani nationality, they can also let you keep both and still stay legal. Practically, its upto the mood of the individual case worker what to ask for.

I know at least a dozen people who weren't asked to leave their current nationality and were given Polish citizenship and they are all of course non-EUs.

I would still suggest not to give up your Pakistani nationality.