I have had exactly the same experience recently
had repeated letters for years and now this …. Also confused by the advice here as I too thought ignore was the advice.
not sure how a Backdoor ccj can happen if they are sending to an address you’re contactable at.
Btw when I say I went to the bank I didn’t expressly say I was leaving the country I asked if I could adjust payments to a plan as my job may be in 2 locations as I didn’t want them to panic and freeze my account.
As it’s not a criminal offense anymore though is there actually anything they can do?