PIP back pay for a year and savings

After an entire year i finally got my pip reassessment result in. Whilst it should have been a very happy thing after moving from low rate mobility to enhanced on both, only then the panic started. I had some saving in my account, less than the dwp thought as i havent updated them for ages. This was activiely going in their favour as they think i have more than i do. Anyway with the letter came a years worth of back payment, although by my maths theres a bit more to come possibly on next monthly pay. So it now tips the overall total of my money right up there near the scary 16,000 cut off if the dwp go by the last figure they had off me, which is now lower. Im scared im about to lose esa, housing benefit and council tax benefit all because they back pay a whole years worth. After recieving letters from the council saturday which are just that dwp have told them there is a change in my benefits, am scared dwp will do maths and tell them i have too much, although in reality i dont.
Anyway long story short will the dwp class pip backpay as savings, or am i potentially entering into a complete nightmare?
Any help would be greatly recieved

Thank you Gary, thats a big relief. I keep evidence for anything out of my usual. I'm no good at spending big amounts anyway but if the statements can't explain it then I add the paperwork every update with them.