I married under the regime of the community property and then adopted that of the universal community. My husband is deceased. The bank asked me to pay a credit of which I had no knowledge and which my husband had contacted alone. Do I have to pay it back

By taking out a loan without your consent, your husband could only pledge his own property and income. Thus, the creditor could not and can not even after dissolution of the community seize a common good. However, he can seize your husband's property that was his own on the day of his appointment.

There is, however, one exception to this principle: borrowing for household maintenance and the education of children are common, provided that they are of a modest amount in relation to the needs of the family. The debt thus contracted by one of the spouses obliges the other jointly and severally. Also, to ask you for the repayment of the debt, it is fundamental for the bank to prove that the debt contracted by your husband fits into this framework.