Why am I not allowed to sell ?

Hi there,
I am a professional photographer.
And my photos are sold in Shutterstock and many other markets.
But I do not know why I have filled out the application form for sale on this site for months and I have not received any answer ?!
I have done this many times and I have been waiting for the news for months.
Has anyone had this problem before?
And how did you solve this problem?
Thanks