Simple. Replace the "||" in your condition with "&&".

} while( ($make_account ne 'y') && ($make_account ne 'Y') );
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Now, it's not possible for something to be the same as 'y' and as 'Y' at the same time. Thus, always at least one of the subconditions will be true.

Alternatively, using De Morgan's equivalences, you could replace the last line with

} until ( ($make_account eq 'y') || ($make_account eq 'Y') );
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