Help with getting account statement from Kensington Mortgages over 6+ years

Na5Apr20

Hi, I'm wondering if someone can point me the right direction.
I wanted to know if it was possible to get copies of old mortgage statement from Kensington Mortgages. I have contacted them directly and they have said that we had an account with them over 6years ago and therefore they no longer hold any information.
 Is there anything that I can do or is there another way of obtaining this information?

Here is a little background to situation:
I had a mortgage with Kensington Mortgages back in 2006, I lost my job and experienced financial difficulty and the house was repossessed. I was going through a difficulty time with a new born and therefore not able to be on top of things. 
I now know that Kensington Mortgages had been applying excessive charges (I know this from old bank statements) and a possible early payment charge on to my account and I wanted to make a claim. For some reason I do not have any paperwork related to this property or a final summary, but I do have old bank statements showing payments ( with account number) being made to Kensington Mortgages. Is there another channel that I can explore to obtain this information.

Any advise would be helpful.

Many thanx