This is how this works: if you don't have a balance due, then <@XXXEFDate> will not have a value, which makes sense because there is no EF deadline for you if you don't owe. So the original letter has that whole paragraph conditioned upon having an EF date, and that's why the original letter has  [@XXXEFDate] at the top of the paragraph, see picture.

So if you put that conditional back it'll work fine. It'll print the paragraph, with real values, when you have balance due and it won't display the paragraph at all when you have refund.