Universal Credit keep investigating me

Last year Universal Credit asked to see 3 months of bank statements. As I am autistic I thought I was OK with £10,000 in my bank but soon learned that was not correct. This triggered UC asking for all my statements for the whole 3 years I had been claiming. Once they were satisfied they charged me a back payment and fined me. So 9 months later, despite me voluntarily sending in my latest bank statement every month they looked into my finances again. Now, less than 3 months down the line I am being investigated again.
I feel like I am being penalised because I am able to save.
I have several large expenses coming up so will be needing large sums of cash soon. However because I can’t draw it out yet it is causing me problems.
Part of the problem 3 months ago was because my PIP payment went up and they gave me a back payment. UC took this into account initially but the month after they continued to pay me the lower amount as they then classed it as savings.
When I queried why I was being investigated again so soon I was just told that I was being investigated by a different apartment this time.
I feel like I am being hounded and it is making me very nervous and uncomfortable.
I don’t drink, smoke, or play the lottery, I’m just careful with my money.