Where are $UIDholder, $indexmonths, $indesxmonths, $indexyears defined?

The OP says in a later post that they are defined at the top of the program.

Why are you calling bind_columns on a statement handle without placeholders?

bind_columns() binds the select columns to variables, and affects where the data goes during fetch(). You are thinking of bind_params(), which binds placeholders and is called before execute(), and you usually don't even need to use bind_params() explicitly since you can supply the param arguments directly to execute().