I renewed my subscription to Lingo Newydd over the phone the other day (so that I wouldn't have to send credit card details by email), and told them about my new address in the process.
95% in Welsh, though I needed a brief translation a couple of times to make sure I was understanding them correctly.
Two phone calls: one to be told that the person to speak to wasn't in at the moment(?) and to call back in about an hour... I only understood something about awr but since that seemed to me to be the point of the message I didn't worry too much. The second one worked out more or less all right, though I didn't catch the bit at the end when she said she had renewed (adnewyddu) my subscription.
Still, I felt like I could pat myself on the shoulder for doing it mostly in Welsh!
(Well, when I spelled my address for them, I went "aitch - eye - tee" etc. rather than whatever the Welsh names of the letters might be. But still mostly Welsh!)