I recently obtained a new passport, the old one having the information of my guardian as I was under age , When I left my country after getting it, I used the new passport as it is the current one, but I entered Turkey using the old passport, as I have a permit card that has been registered under it. Could this be a problem? What can I do? I must go and let them know of the change. I have been to the embassy of my country, and they gave me a supporting document informing of the change. However, would the stamp in my new passport showing I left my country be a problem, as the entry stamp from Turkey is in my old passport?
As long as your old passport has a valid endorsement (like a visa stamp), you should carry it with you.
At the border, ask the immigration officer if you need to transfer the visa to your new passport. Sometimes, they don't need you to as long as you carry both passports with you.