Not sure what brand it is.

But yesterday it started opening only half way up and I couldnt get my car
out!

I thought the manual string pull looked like it was caught up and tangled in
the motor - as there doesnt seem to be friction with the door sliding
down...

then when I finally close it, the door immediately goes up again. Which is
scary given tools and bikes etc are in the garage.

Easy fix or serviceman time?