ESA compliance interview

I recently was told to attend an interview with a compliance officer regarding my ESA claim.The letter said 'We're reviewing your benefits and circumstances.
I have had a medical for ESA last year and was allowed to remain in the support group. I have also gone through the PIP process transitioning from DLA. I was awarded enhanced rate for my daily living needs, and standard rate for mobility.
I have Borderline Personality Disorder, including agoraphobia, depression and anxiety. I have great trouble meeting people and going out. My 21 year old son accompanied me to the interview, and previously was with me for both the ESA and PIP medicals.
I met with the compliance officer who said the problem was my son living with me, as they have been paying me 'Extra money because you are severely disabled'. They said this should have stopped when he turned 18.
I had absolutely no idea this was only paid for a single adult claimant. I had no idea that it would be stopped when he turned 18.
I have always notified the council & tax credits when he started work, etc.
I have even spent the last 3 years paying off a child tax credit over payment, because my son finished college in June 2013, and was going to continue at college for the second year dependent on his passing the first year. He didn't get the results until Sept and hadn't got the marks to do year 2.
The child tax credit dept said I had to pay back money I had been paid since June when his course finished, even though we had hoped his education was ongoing.
He luckily found employment, but it meant that from June, 3 months earlier we weren't entitled to Child tax credits, even though we had no way of knowing that he wasn't continuing education until the Sept results just before term started. This meant we would have had no money for him.
I explained this to the compliance officer, showing the Child tax credits office knew my son's age and the fact he was working since Sept. I had also notified the child benefits of the change of circumstances, so that money stopped. I told the council and our housing association when he had started work. I also clearly said my son is my main carer who lives with me in both ESA and PIP forms.
I had no idea I had to inform the ESA again when my son turned 18. As I said before, I thought that ESA was paid for me, and child tax credits were for my son. The 'Extra money because you are severely disabled' has no mention of being paid if I'm the only adult in the household.
Every agency has known my sons Date of Birth from my claim forms. The compliance officer admitted that his department hadn't sent any letter to me since 2011, yet I had the medical for ESA last year?
I know that changes of circumstances need to be notified, but I thought that was like if I commenced work, started living with a partner, or if my health changed, etc. Surely my sons age is on their system, as it was for the child benefit agency, the council and child tax credits.
The compliance officer told me I would obviously not be paid the benefit for being severely disabled (£62.45) anymore. I completely understand that. I am just left in limbo now, not knowing if I will have to repay the money I have been previously receiving.
My point is that it is not revealed that this payment is only paid to a single adult claimant on any of my ESA letters. I have proved that I have notified changes in circumstances, and would defiantly been in touch if I had been aware.
So far I have received a letter saying my money has been reduced from £188 to £125.55 from 29/09/17. I have not heard anything about whether or not I must repay the overpayment. The compliance officer was understanding, and could see I was truthful and totally unaware of any wrong-doing. I am praying that this matter is resolved now and I have nothing to repay.
I just wanted other members to make sure they are aware of this matter. Hopefully my story will prevent someone else finding themselves in trouble due to not being aware that the severe disabled payment is only being paid to single adult claimants.