DWP knowingly sent incorrect letter about termination of IR ESA

This is not seeking advice, as much as it is a warning for others who may receive these letters.

In October 2019 my family and I moved area to one that we knew was UC full roll-out, but we planned and prepared in advance. We applied for UC before we moved, had to make a few journeys to sign paperwork and provide evidences etc, but facilitated the transfer as much as we could.
There were still a few hiccoughs, and some issue where UC originally said my ESA would not transfer so I would be expected to work, but after speaking to ESA, PIP and UC multiple times the issues were all closed and my claim was awarded for UC with no requirement for work-focused interviews etc.

I would like to state here, slightly irrelevant to ESA, but my award for UC is slightly higher (not much) than the total of all legacy benefits I received, so it's not all horror stories.

My surprise, however, and the reason for this discussion arrived in the post on Friday 07th February 2020, when I received two "Changes in the Employment and Support Allowance rates payable" letters both dated 1 February 2020.
One letter showed the new rates after April 2020 when the inflation rise will occur.
The other letter clearly stated that, following a claim for Universal Credit (October 2019, as I have stated above), the DWP were terminating my claim for Income-related ESA from 06th April 2019 (almost 6 full months before our UC claim), meaning that there would be an overpayment and overpayment recovery.
I was horrified, indescribably anxious, and unable to focus on other tasks. My wife, who is also my carer, had to try to calm me down while also battling her own anxiety about what the letter could mean for us.

Needless to say, we decided the best option was to ring the DWP to ask them to explain what was happening and, after a 30 minute wait, I spoke to a pleasant woman in the Midlands call centre who simply stated
"There's a note on the system for you to ignore the letter, the advisor could see it was incorrectly generated but authorised it to be sent".

How could it have been generated in error, when it has my all of my contact details on it?
Had they drafted this letter terminating my claim but never sent it for some reason?
Why did they still send it if they knew it was incorrect?
Why did they not send a letter to arrive with it explaining the error? Or, even a phone call to apologise and say it would be arriving within a week?


It is more boggling because there was no apology from the DWP, no acknowledgement of stress caused and no proof the letter is false other than my phone call to the call-centre. Had I not rung then my wife and I would be spending the next few weeks living in fear of a letter demanding back-payment or sanctions on our current benefits.
The DWP ESA team just seems to not care.

I apologise to anyone reading who may feel this was a bit of a rant, I accept that it was a slight ranty but I do not know how many other people out there may have also received blatantly incorrect letters from the DWP that they have had to investigate only to discover they have notes on the system saying to disregard the letter.