So glad you've found out what the problem was/is. It's must have been very frustrating and worrying.
I had a company that changed my postcode when I first moved in 5 years ago. Their parcels always had the same error and were wrongly delivered. I came to the conclusion that their software - the type where you click on the first line of your address - was a) old and b) had errors in it. I was very unlikely to have made the same error, just with one company, every time I filled in my address!
I had really forgotten about it and used the same company, who did it again, recently. It seems that although I put the right postcode in, the drop-down software automatically changes it. So, again an assumption on my part, they may not have yet updated that software. I just don't use that company any more but you are not in that position, sadly.
You could ask if the automated address finder is to blame as, if it is, it will go on doing it until the error in it is corrected.