What information do they have to give to a debt collector?

They have begun sending letters asking me to resubmit my income/expenditure. Do I have to do this? Can they do anything if I do not give them this information and just continue with my current payments? Everyone was happy when the arrangement was set up.
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Ellen:
I wasn't as happy as before and I just stopped feeling motivated.
(10 November 2016)

Ellen:
Ever since I was in 6th grade something in me felt broken.
(10 November 2016)

Ellen:
I've also been very sad for the past 4 years.
(10 November 2016)

Ellen:
I've had problems being around men since then.
(10 November 2016)

Ellen:
I've had problems for years, starting when I was about 4 or 5. I watch my stepfather at the time abuse my mother.
(10 November 2016)

Chang:
I like this girl a lot and I believe she likes me I really want to be with her and I don t know what to do these last couple of days I ve been highly depressed and not able to focus because she s all I think about please help.
(10 November 2016)

Chang:
Her mom saw the text which were not inappropriate in any way at all and found out we were dating so she made her transfer to an all girls school which is about only 3 minutes from my school.
(10 November 2016)

Chang:
She would text me on her mothers phone because her parents do not allow her a phone.
(10 November 2016)

Chang:
But her parents are very religious and do not want her dating which I didn t find out until we were dating.
(10 November 2016)

Chang:
So I ve met this girl and we ve been really close so we started to go out.
(10 November 2016)