Choose the correct options to complete the dialogue

Anna: Hi, Sam. I called you yesterday. You didn't answer me.

Sam: Hmm… That's strange. When did you call me?

Anna: At half past six.

Sam: I [swim|was swimming|were swimming|will swim] at that time.

Anna: But I also called you at seven o'clock. Your grandma [answer|answered|will answe|answering] me.

Sam: What did she say?

Anna: That you [was walking|will walk|were walking|walk] with your friends.

Sam: No, she was wrong. I [were sitting|was sitting|to sit|sitting] at the cafe with my mum and dad. We were celebrating mum's birthday the whole evening.

Anna: Why didn't you call me back?

Sam: I [wasn't doing|were doing|was doing|did] my homework from 9 to 11 o'clock. I was very tired and went straight to bed.