As Dr. B mentioned "was taking" is correct. We use the past continuous for something which happened before and after another action or for something that happened before and after a specific time (when I was 21 ... one day). "Used to" is used when we talk about things that happened in the past (habits) but don’t happen anymore. I hope this helps.

"Was taking" means there was one action that lasted pretty long. If you say "used to take" it will mean you performed the action several times and it was a regular one for you at that time. Have a look at these examples: I was reading a book when you phoned. (At that time the action was in progress and it's a single action you refer to) I used to read a lot when I was younger. ( Reading was a regular repeated action in the past, but it doesn't happen now, at least you don't read as much as you did in the past)

Was taking