When you received the device, you can either do ON DAY 1
1. Go to online chat or call Voda give the 30 days notice, do not say the word CANCEL, then you could pay max 1 month airtime fee 20, 31 or 42.
2. Request PAC/STAC, then port the voda data number out straight away or on day 15 (more safe), then you just pay the days you used before port out.
For myself, I got my PAC on day 1, port out few days later, final bill £-35 (£42 tariff)
If you were told you can't give notice or request pac bla bla, just f off, change another person.