My mom died last year & has credit card bill unpaid. My dad is partially-paralyzed. Am i required to pay it?

The credit card collector is bugging us though our home phone & sent several letters threatening for fraud. We sent them a letter informing them that my mom is already dead and we can only pay them 500 pesos a month. They've sent a conforme letter which we didn't sign but we've paid for only 2 months for times are hard & we couldn't continue the payment now.