Three
This number is listed by Three on its own website (Three Business customer support (337 from a Three Business phone)).
Source: “337 from your Three Business phone 0333 338 1004 from any other line” (opens in a new tab). Checked 13 October 2026.
This could still be a scam call
Criminals can make their number look like a genuine one (this is called spoofing). If someone calls from this number and asks for money, bank details, a code or passwords, hang up. Then call Three back on a number you've found yourself, such as the one on their own website or on a letter or bill from them.