My boss ( relative's friend ) calls me to work urgently & overtime (no pay )and i can't refuse for some reason . I am being exploited.

intj here , when I work i want to do it perfectly and flawlessly. I am a new intern and my boss gives me work after work hours and during Sundays and I do it . I do not like it , but for some reason I subconsciously do it .

Today i took a leave from work , my boss gives me work at last hour every freaking time . I would do the work then he would say to make changes and he phone called me again & again . But I did the job. Afterwards I was so pissed off that I yelled at my family and i feel bad.

My sister also works (part time ) but she never picks phone after hours /etc is this issue due to my personality traits and if so how can I improve it. I don't want to be that person who does the job and is frustrated and destroys relationship with family in near future.

Tbh , things has gotten bad i had an exam I wanted to give for future carrier but didn't prepare for it due to ts taking my remaining energy & attention.

If you were in my shoes how would you deal with the situation ?