Three bills in advance for your plan and in arrears for anything used outside it. That mix is why a single monthly charge can contain two different periods and end up matching neither your plan price nor last month's amount.
The first bill, and the last one
Your opening bill covers a part-month from connection plus the first full month ahead, so it is larger than normal. Your closing bill works the same way in reverse and often surprises people more, because it arrives after they believe the relationship has ended.
A final charge after you have left is normally the notice period plus any outstanding device balance. Cancelling a Direct Debit at the moment you switch away is a common mistake: the final bill still exists, and a missed payment on a telecoms account can be reported to credit reference agencies.
Roaming and travel
Three historically built its brand around inclusive international roaming, and the terms have changed over the years. Different plans carry different roaming entitlements, and destinations move in and out of inclusive lists. Older plans sometimes retain more generous roaming than newly sold ones.
Roaming usage can also appear on a later bill than the trip itself, because usage data from foreign networks reaches your provider with a delay. A charge relating to a holiday two months ago is not necessarily an error.
Where an unexpected amount usually comes from
- Check the itemised bill in the Three app, which separates plan charges from usage charges.
- Look for data add-ons purchased when an allowance was exhausted.
- Check numbers outside your allowance, including premium rate, non-geographic and directory services.
- Check for a mid-contract price rise applied earlier in the year.
- Check whether a device plan has ended, which lowers rather than raises the bill but changes the amount you are matching against.
If the charge is on a card rather than Direct Debit
Pay as you go top-ups and add-ons bill to a card and appear as ordinary card transactions rather than as a monthly bill. Automatic top-up, once enabled, will keep charging whenever the balance runs low, which can look like a repeating unexplained charge if you have forgotten it is switched on.