mine add as numbers.
yours may look like numbers but they might be text
make a copy of your workbook and try things
like
= A1 +A2 see what you get
if zero
=value(A1)+Value(A2)
if still zero
=value(trim(clean(A1)))+value(trim(clean(A2)))
If still zero you probably have non printing charaters which you will have
to identify to remove before you can add them