i dont know how to call it

I have the following data.

 df_a <- data.frame(id=c("John","Ben","Bill", "Eminem"),
                     amount=c("300", "500", "1000", "1200"),
                     issue_date=as.Date(c("2010-01-01","2011-01-01","2012-01-01", "2015-02-01")),
                     last_pymnt_date=as.Date(c("2013-02-01","2012-05-01","2014-01-01", "2018-02-01")),
                     months_passed=c(37,16,24,36),
                     term = c("36", "36", "36", "36"),
                     status=c("Fully Paid",
                              "Charged off",
                              "Does not meet the credit policy. Status:Charged Off",
                              "Does not meet the credit policy. Status:Fully Paid"),
                     stringsAsFactors = F)

    library(DescTools)
    df_a$maturity_dt <- AddMonths(df_a$issue_date, 36)

I want to make the last_pymnt_date same as maturity_dt if status variable includes the expression "Fully Paid". If I run the following line it makes last_pymnt_date variable some numbers.

df_a$last_pymnt_date <- ifelse(grepl("Fully Paid", df_a$status),
                               df_a$maturity_dt,
                               df_a$last_pymnt_date)

Any suggestion?

Thanks