Interrupt is activated as soon as I insert a jumper wire into the port
Connect both Pin2 and Pin3 with two 1K resistors to ground.

When a pin that's set as INPUT is "floating" (it's not connected to anything) the value on it is "undetermined" and interrupt can trigger when a neighboring pin status changes, or even just magically by itself. The 1K resistors (called pulldown resistors) will make sure that pin is set to LOW when it's not connected using the jumper.

This circuit should put a stable 0V on Pin3 when switch is unpressed and 5V when it's pressed. You should be able to verify that using any voltage meter.



If the issue persists then swapping the microcontroller on the Arduino is just one of the steps you need to perform. You would also need to burn a bootloader on the chip. It's not a hard procedure but it requires a second Arduino.