Jobcentreplus have lost my accounts!!!!!!!

In January I started my own small business through the NEA scheme, its small but profitable. The reason I started the business was to get off benefits, in 2014 I was diagnosed with a cancerous brain tumour, I've had surgery and radiation to prolong my life but there is no cure and no options left. I was told by various professionals including the job centre that I would never work again and I am proving them all wrong by doing this. Due to my health condition my wife is my carer and she receives income support and carers allowance. Because I'm self employed I need to send my accounts every 3 months as evidence of my earnings to income support for my wife's benefits.

It is very fast looking like all the confidential information we posted has gone missing, income support are claiming to have never received it. I was wondering who is responsible for my documents after we post them Royal Mail or DWP, they are sent in the job centres own envelope as requested, we seal the envelope with extra sellotape for security.

I am absolutely fuming at the moment, I run a small online business reselling products bought from wholesalers for a profit and somebody potentially has a copy of my accounts and other personal information relating to my business.

What action can I take? I am holding off picking the phone up because I am so upset about this matter!!!!!!!

Thank you for any advice you may be able to offer.
Mark