"the only people in the country that have my new address as flat c when it is actually flat 3."
A 'friend' had been trying to sign up for HP's Instant Ink subscription or a few months.
The address is in a block of 1970s flats with around 40 flats all with the same postcode.
Friend had tried signing up online, several times, each attempt had mysteriously failed with a really hellpful error message e.g. "An error occurred, pleas try again later".
Eventually the friend gave up and called the support phone line and the helpful (yes, honestly) person talked through the process for half an hour or so.
One of the various problems was that whatever address database was being used didn't want to allow flat numbers *at all* for this postcode, although every other address database for every other online application allows (or even requires) the entry of flat numbers.
Maybe HP Ink have outsourced their order processing to Crapita. Or vice versa. What a combination that would be.