ESA change of circumstances.

Hi guys.
I am hoping that someone can advise.
I am a single parent of two dependant children aged 15 and 12. My eldest son turned 18 in May and is in employment earning around £200 per week. He was supposed to go to university but gave up after a week
I claim child tax credits for two children and child benefit.
I also recieve Pip enchanted rate for care and mobility as I have a progressive illness
Nobody claims careers allowance for looking after me. We soldier on somehow.
I am also in the support group for ESA and recieve an extra amount with that for being disabled. I used this extra for help within the home as I am finding it increasingly difficult to manage.
We live in the ex husbands property but cannot claim housing benefit because the children are his. I pay him rent. He lives overseas.
I am under the impression that I will loose this extra amount( severe disability premium & disability income guarantee) because I have an 18 year old son living at home.p
So I contacted esa on the number on my award letter to inform them that my son has turned 18 and working as i assume it is a change of circumstances. I did not want to find myself being overpaid. The chap I spoke to hadn’t a clue and said he would pass this info onto the relevant department
Please could anyone advise me if this could trigger my benefits being stopped and me having to reclaim ESA or even worse Universal Credit.
I am extremely confused and anxious about this whole situation.
I am wondering if someone can advise me as there seems little information online. Should I follow my call up in writing or just wait.
Thankyou

Thankyou Gordon for your reply. I am hoping that they do not suspend my ESA whilst they sort out my claim as it is only a case of stopping the extra amount surely. If they do suspend payment, will they back date it when it is reinstated? This whole benefit system is a minefield.
I will keep an eye on my bank account and probably follow up with a letter this week for peace of mind.
Is there anything I can claim in the meantime. I do not have anyone to claim careers allowance as It’s just myself and the kids.
Thankyou Gordon

Thankyou Gordon.
If I follow up my phone call by putting the change of circumstances in writing, do I send the letter to the address on the letter where my esa claim came from? Ironically the Center who dealt with my claim is down in Wolverhampton and I am Lancashire. It’s so. I am terrified of everything being suspended whilst they sort a simple change of circumstances out, especially so close to Christmas. I am sorry to be a pain with all my questions.