Can the council make me pay back all the rent they have paid to me because I rent a house from my mum's partner

I have been recieving various letters since I moved my new partner in to my house. They are saying I owe £14,000 this is basically the full amount of all the housing benefit payed by them. I have tried to send them numerous proofs of paying this but because I paid most by cash I'm finding it difficult. The council now are requesting all my bank statements from last 7 years which I don't want them to see it's my personal information. 

Do I have a right to tell them I don't want them too see this information? I feel they are trying to bully me to get the money back. 

What are my rights please I feel cornered?

Thanks for reply in advance