1. I called you many times, but you didn't answer.
=> You called many times.
Infinitive: unrealized (hasn't happened)
2. I tried to call you many times, but you didn't answer.
=> The calls didn't go through; something was wrong with your phone; the calls weren't connected. (Note, the last part ...but you didn't answer doesn't fit the semantics. Compare, I tried to call out, but I had food in my mouth at the time, so I couldn't; I wasn't able to call out; it didn't happen.)
Gerund: realized (happened)
3. I tried calling you many times, but you didn't answer.
=> You attempted ... many times.
Does that help?
- For Teachers