[ordeal]

Hi!
I've found some examples that show the difference between could and was able to.

- We use could have to say we were able to do sth, but in fact we didn't.
He could have helped me, if he'd tried. (= but he didn't)

- For general ability in the past we also use was able to, though could is more common.
I could/was able to swim when I was five years old.

- For a specific event showing success after trying, we use was able to, managed to, or succeeded in, but not could.
I was able to/managed to solve her problems for her.

- We use couldn't have to say we were not able to do sth so we didn't.
He couldn't have helped me anyway. (= he didn't)

I hope this will help you. Good luck!