My uncle has asked me to be a witness for him to get a loan from one of the banks. This loan involves riba. Please note that my father and my uncle are partners in this loan, and when I refused to be a witness, this caused problems. So I acted as a witness even though I was not happy about it. I regret what I have done and I feel bad about it. Now I am confused and feel constantly depressed. Please advise me.

Praise be to Allaah. 

It
is forbidden to act as a witness for riba-based transactions. You have to
repent and seek the forgiveness of Allaah for what you have done when you
witnessed this riba-based loan.

And Allaah is the source of strength. May Allaah bless our Prophet Muhammad and his family and companions, and grant them peace.