Assistance canceling my phone contract due to moving abroad

Despite having sent certified letters containing all requested data, I have yet to receive any confirmation of my contract cancellation. Moreover, the company at both its stores and customer service hotlines failed to provide the information that to cancel direct debit requires yet another letter I am certain O2 will ignore, despite being required to sign for its receipt. Since there is nobody available on the English hotline that can do anything other than open a ticket, which O2 does not respond to, I am trying all avenues to get this resolved before I leave the country on Saturday. It should not take 3-months to get a straight answer.