I didn't have any luck with checking the voltages, they were all over the place.
However I made a poor man's "oscilloscope" using the arduino's ADC (just analogRead the pin in the loop) to check the output values again (I don't have access to uni labs for a few days) and this is what I got for the working phase:

Also the fact that it doesn't go all the way upto 1023 is the LDO which drops the voltage down a bit, but it's clearly a logic level signal going high and low very quickly.
now this is what I get for the broken phase:

The signal is not amplified at all! it's clearly going high and low but in a much more analog fashion that usable data. the circuit is clearly biased in the midway point (about 512) and going up to about 530, and downto 500 which I'm assuming is the raw signal output from the sensor.
This really confirms the fact that I've killed the NPN transistor there. (please post if you know a method to test it in the circuit just to make sure it's dead). I tried having a look on
https://uk.rs-online.com/web/ and they don't have the SMD version of the transistor.(Mouser, digikey, etc are out of question as they would charge an arm and a leg for shipping with an order like that). do all other jelly bean NPN transistors work? or is there some parameter I should pay attention to when buying one? I really want to get this circuit working asap, thanks.