How to respond to 'sorry'?

Tina: I am sorry, I didn't call you last night.

Ryan: That's(that is) okay.
             Or
            That's okay. No problem.
            (Here by saying 'no problem' you are trying to be kind.)

Tina: I got busy cleaning the house.
           Or
           I got finishing my work.
           Or
           I got finishing the chores.
           (Here 'chores' means work related the house.)

Ryan: That is understandable. You had a busy week.
            (Understandable means "I can understand".)

Tina: Thanks for understanding.

Ryan: Don't worry, I slept early anyway.
            (Early means ' before usual or planned time. If Ryan usually goes to sleep every night at 11pm, yesterday he slept before 11pm that is at around 10pm.)
(Anyway is used to confirm a point what you just mentioned.)