Theofanis Markopouliotis

Hi, I submitted a self-assessment form in September that initially quoted me an amount of tax owed. Two weeks after, the amount was doubled. I think I know what the issue is, and I was supposed to have received a letter from HMRC that would tell me how to dispute the amount. This letter never arrived after 6 weeks. I am at present unable to dispute the amount via a phone call, and have no means of accessing the post address where I am supposed to send my dispute given I never got the letter. I need help either in the form of a physical address or a phone number than I can use to discuss this with someone that is qualified to discuss my case. I have spent more than 6 hours on the phone with HMRC, costing me more than 100EUR in phone charges as I am outside of the UK at the moment