Adultery and domestic violence

My parents have been married for the 21 years and since the last 8 years my father has been raising his hand on my mother on several occasions. Four years ago he cheated on my mother with a lady in our family and his relationship went on for one year but he was caught by me, his 16 year old daughter then. We did not take any legal actions because my mother is a housewife and we do not have a source of income. Last year again he was in a relationship with someone but that’ did not last very long because my mother had realised about it and this one wasn’t a sexual relationship. But this time for the past two months something has been going on but we are not able to find a proof, I am currently 20 and I am a second year law student myself, but I will be needing a legal advice. We have seen him staying out for more than 8 hours a day during the pandemic and he has bought a contraceptive which my parents do not even use. Is there a department which can help us keep a track of his phone and where does he go because his phone is locked and he has two numbers.