Short answer. From the creditor, not the debtor. Article 2070 says that if you paid as guarantor without notifying the debtor, and he, unaware of your payment, paid again, you have no remedy against the debtor — only against the creditor, who now holds double payment. Your failure to give notice caused the overlap.
What the law says
If the guarantor has paid without notifying the debtor, and the latter not being aware of the payment, repeats the payment, the former has no remedy whatever against the debtor, but only against the creditor.
Civil Code, Article 2070 — Double Payment. Read the full provision →
When the debt gets paid twice
This is the classic trap of paying a guaranteed debt in silence. Article 2070 addresses it head-on: If the guarantor has paid without notifying the debtor, and the latter not being aware of the payment, repeats the payment, the former has no remedy whatever against the debtor, but only against the creditor. Two payments have reached the creditor for a single debt — yours and the debtor's — and the Code decides who bears the tangle. It does not spread the loss; it points the guarantor firmly at the creditor and shields the debtor entirely.
Why the debtor is protected
The debtor did nothing wrong. Not knowing that you had already settled the obligation, he paid a debt he reasonably believed was still outstanding. The failure lies with the guarantor who paid without a word of warning, and the law places the consequences where the fault is. To let you recover from the debtor would be to make him pay a third time — once to the creditor, and again to reimburse you — for a debt he only ever owed once. That is exactly the outcome the article refuses to allow.
Recovering from the creditor
Your remedy runs against the creditor, who has now received full value twice over and has no right to keep the surplus. Having been paid the whole debt, he holds the second payment without any cause, and the guarantor may pursue him to recover it. This is the practical reason the notice requirement exists: had the debtor known of your payment, he would never have paid again, and there would be nothing to unwind. The creditor's double recovery, not the debtor's pocket, is the fund from which you make yourself whole.
Avoiding it, and the narrow exception
The entire problem is prevented by notifying the debtor before you pay, so make that your invariable practice and keep proof of it. If the double payment has already happened, direct your claim at the creditor and preserve both payment records to prove the debt was satisfied twice. There is one slim exception worth knowing: where the guaranty was gratuitous and a fortuitous event prevented you from warning the debtor, an insolvent creditor can open a route back to the debtor — a separate situation with its own strict conditions, not a general escape from this rule.