Assalaamu alaikum wa Rahmatullah Mufti Saab,

The question is regarding the validity of marriage.

Five year ago, I liked the girl and she also liked me. I sent the proposal for marriage through parents. Initially, her parent's resisted and somehow, they agreed for marriage after the girl talked with the parents. Within a couple of months, we got engaged.
Due to financial conditions, our parents decided to postpone the marriage for a couple of years. In these years, we used to meet a lot and somehow, we got to know that it is not legal to meet even after engagement.
I got to know from the Imam of a nearby masjid that, girl can marry a boy in the absence of her father/brother if they are adults.
We chose her step-cousin as her vali and one of our friends became qazi for marriage. Mehr amount got decided between us. So, basically we got into nikah without any paperwork and our parents weren't aware of this nikah. (Just to be clear, our parents agreed for our marriage at that time).
Now in the present scenario, the girl's parents want to cancel this marriage. Girl tried to convince her parents and even my family and I tried to convince them. They are not agreeing for the marriage. Now, the girl wants to proceed with her parent's decision and now she believes that our marriage is null and void as she watches some sheik's videos online. I didn't get any scenario for the continuation of this relationship.
Now, I'm confused. Is this marriage valid and Do I need to give divorce to her for this marriage?
Kindly provide me fatwa in this regard.

Jazaak Allahu Khairan Kaseera!
May Allah bless you for your service for the ummah. Ameen!