Terrible account cancellation service

I have had an incredibly difficult time trying to cancel my contract. Initially I went to a Vodashop and was told to phone the cancellations department because apparently the staff members can't help you face to face which is absolutely ridiculous. I called the number I was given and I received a cancellation quote which I proceeded to fill in and submit within the 14 days it is valid for. I have now just received an email to say that the account I cancelled in April is in arrears. I made certain to cancel my contract before I left the country. I paid the outstanding balance and faxed (there is only a fax number, you can't email) the proof of payment and a signed copy of my acceptance of the quote for a premature cancellation as instructed on the quote. I also used the reference number I was given when I made the payment. I am absolutely disgusted with this shockingly bad service.