UC financial review help

Ive sent all of my financial statements for the previous 4 months as requested, after having trouble with a few where pdfs of the transaction dates (that I had created on the banking websites) incl all the financial institute info and my info were visable were rejected by the UC advisor. In the end I went into branch and got some stamped statements. However, I am still waiting for a statement for my saving account from Santander. There isnt a branch anywhere near me so i cant go in. Its an Instant Access and they are usually produced annually, the account has only been open a few months. I called to request them on the 11th (after mine was rejected) and none came, I called again on Monday to be told that the office that deals with them would be unable to produce them as they are done annually. I then called the complaints department who said they would send another request and they thought the issue was that my statements were set to webmail instead of post. Which they changed. UC have extended the 'to do' list until the 27th to allow time for the statement from Santander to arrive but what if it doesn't? I'm panicking like crazy, it's really stressful and I keep thinking worse case scenario. Can they stop my payments if I can't produce it?