IS10 FORM

Hello everyone. I would like to let you know that I received a letter on 21/02/19 requesting me to contact DWP pertaining to information they needed in regards to an IS10 form. I spoke to a lovely gentleman who filled out the form over the phone and he then told me it would take 6 days to process.  I burst out laughing as ALL my previous dealings with the DWP have been truly traumatic. He told me that I would qualify for something called Supreme Disability Premium, which meant that I would get an extra £64.30 pw, well I was surprised and thanked him for his help, but I wasn't going to hold my breath.
Well imagine the shock when I accessed my bank account this morning, for other reasons, to see that there were 3 transactions from ESA totalling a massive £12 387.20. 
I thought this had been an error and contacted them straight away. An error hadn't been made...it's real....it's mine and I still get a further £64.30 pw. This had been backdated from 2015. Your future benefits are not affected by this amount in your savings account as this is an official error, which is given a total disregard' Different rules apply if amount is under £5000.
Thank you to all of you have given advice. poppy123456 keep doing what you're doing. For any of you who are still waiting for a response or who have been let down TIME and TIME again, I will be praying for you and would say NEVER EVER EVER GIVE UP.