Notifying a change of terms and being able to prove it: certified SMS
· 3 min read
You raise the price, change a feature, update the terms of service. Months later, a customer disputes a charge: “nobody told me”. If the communication was an email, the conversation you are in is about spam folders. If it was a certified SMS, it is about an evidence file with a delivery receipt.
Why the channel matters
In ongoing contracts —utilities, subscriptions, telecommunications, insurance— consumer law requires changes to be communicated in advance and the customer to be able to terminate without penalty if they do not accept them. The exact notice period depends on your sector; what does not change in any of them is this: the burden of proving that you communicated is on you.
The certified SMS keeps: the full text communicated, the date and time, the operator's delivery receipt —in Spain, delivery to the handset— and, if the customer opens the link, the reading of the complete content on the portal. All of it chained and anchored daily with a qualified Camerfirma timestamp.
The evidential regime, without make-up
It is not a qualified eIDAS service and it presumes nothing on its own: if the customer challenges it, authenticity is proven with the file and, where appropriate, an expert report (art. 326.3 of the Civil Procedure Act). What the Regulation does guarantee (art. 43.1 eIDAS) is that electronic evidence is admissible: nobody can dismiss it for not being paper. Our job is to make the file withstand that scrutiny; this is how it is built.
In bulk and through the API
A change of terms is not notified to one customer: it is notified to ten thousand. The API accepts certified sendings just like normal ones — with idempotency (a retry from your server duplicates neither the message nor the charge) and status by webhook. The certified supplement is fixed per message and is published.
Useful combinations
- Certified notice + acceptance signed with OTP when you need an express yes, not just the communication.
- Certified notice for the change + WhatsApp utility for the later operational reminders, which do not need an evidence file.
How a serious mass notification is organised
First, the list. Export from your system the affected customers with their mobile number in international format. The platform validates the numbers on import and tells you how many can be notified before you start.
Second, the text. The complete communication —the new terms, the effective date, the right to terminate— lives on the portal, not in the SMS: the carrier message identifies the sender and links to the full content, and that complete reading is what gets evidenced.
Third, the sequence. Certified notification today; an ordinary reminder —not certified, cheaper— to whoever has not opened it after seven days; and the cut-off or actual application on the announced date. All three steps are dated.
And the archive. Each file and its PDF certificate remain downloadable in your account, with public verification by code. When, two years from now, someone disputes a charge, the answer is a document, not a search through email folders.