I have tried raising the hotend temperature all the way to 250c but no change really.
250C is way to high for PLA at that temp it should just ooze out. As Neale has said is the thermistor calibrated you could check it with dipping the nozzle in boiling water and see if the temp is around 100C. If the thermistor is not quite touching the hot end that could be another problem.

Going off memory the thermistor should measure about 100k at 20C but they are all different. One way to calibrate the amount going through is to mark the filament say every 10mm for about 200mm with a felt tip pen then instruct the soft ware to send say 30mm then you can work out if it is short or long. without the nozzle on, then when you get it near do it with the nozzle on.

If you have the heat too high it will burn and block the nozzle. Just my two cents worth. ..Clive