Spain's 400 prefix: what it is and how to stop sales calls

Since 17 October 2026, companies calling to sell you something in Spain must do it from a nine-digit number starting with 400. It's the flagship measure of Spain's new Customer Service Law: you know it's a sales call before you pick up.

Numbers starting with 400 can only make calls: you can't call one back. They're not used for customer service either, which must go through other numbers. If a 400 number is calling, it's advertising — an energy deal, a phone plan, insurance — even from a company you know.

But the 400 prefix has an important limit: only companies that follow the law use it. Scammers won't identify themselves; they'll keep using ordinary numbers, often spoofed. So the 400 prefix solves part of the problem, not all of it.

Block-Spam now has a setting for calls with the 400 prefix: with one tap you choose to block them or to be told it's a sales call before you answer. If you want one of them — your bank, say — mark it as allowed and it will always get through.

For calls without the 400 prefix, Block-Spam keeps doing what it always has: it automatically cuts off known spam and scam numbers and tells you who's calling before you answer. It's free and needs no account. Get it on Google Play or the App Store.