Julia appending data to dataframe gives dataframe not defined

Dear all,
I am trying to append data to a data frame. I have set an empty dataframe, then made a copy of it, the point is in populate the data frame and rest it by re-copying the empty one. By doing this reiterate, I save the data directly instead of keeping it into memory:

df = DataFrame(
    column = String[], ...)
CSV.write("df.tsv", df; delim='\t', append=false)
E_df = deepcopy(df)
x = <a subset of a dataframe with the same columns as df>
append!(df, x)
CSV.write"df.tsv", df; delim='\t', append=ftrue)
 df = deepcopy(E_df)

But I get the error
UndefVarError: df not defined
But then if I call the dataframe:

julia> df
4×8 DataFrame. Omitted printing of 2 columns

If I try push!(df, x) I get MethodError: no method matching iterate (::DataFrame) although the package DataFrames is loaded.
What am I getting wrong?

There is a missing ( after write.

Hard to say without a MWE.