Praise be to Allah.
What you have to do is to repent sincerely to Allaah, by regretting this sin, giving it up and resolving not to return to it. You should also pray a lot for forgiveness, and do a lot of righteous deeds, because Allaah says (interpretation of the meaning):
“Verily, the good deeds remove the evil deeds (i.e. small sins)”
This is what will expiate for your sin of looking at and listening to haraam things. With regard to those who say that you have to offer expiation – such as the example you mentioned – for watching movies, he has to produce evidence for that, because it is not permissible to impose something upon the people without sound evidence. Whoever imposes something on people that was not enjoined by Allaah has ordained something in the religion for which Allaah has not given leave. It is not permissible to invent expiations for sins and to specify their type and number without evidence from sharee’ah.
Fasting in general terms, without specifying a particular number of days, comes under the heading of good deeds which wipe out evil actions. May Allaah help us and you to repent sincerely..