The phrase "one of my accounts" should be interpreted as an account opened at Cloudbet. I can not say if I have opened an account at Cloudbet before the day in question prior to 2018. I began keeping better records and can say that I have not opened an account since March of 2018.
An account opened at Cloudbet does not eliminate the possibility that there was
another account in the past that you forgot about. Like you said, you only started keeping proper records in 2018. Based on Cloudbet's reply, they did suspect that it was a matter of multi-accounting. And those things can happen if you are using VPNs.
In the end, it looks like this will end on a positive note. Nothing has been proven and the bookie has decided to settle the matter.