As I understand your statement, your relative received a pension payment in January 2021, died in January 2021 and also received a pension payment in February 2021. And the 2021 1099-R reflects these 2 payments and has the decedent's social security number on the 1099-R.
This seems correct to me. Usually pension payments paid in one month are payments for the previous month. Thus the January 2021 payment was for Dec 2020, and the Feb 2021 payment was for Jan 2021. It is not unusual for a pension plan to pay for an entire month provided the recipient was alive for at least 1 day in that month. This is likely why they received the Feb 2021 payment - because they were alive in Jan 2021.
If this is the case, the 1099-R is correct and the payment amount should be reported on the decedent's final tax return.
I hope this helps
