Query Filtering Problem

I do not want results with combinations like this:

d.workphone is null and m.workphone = '0'

m.workphone is null and d.workphone = '0'

but my query below still brining in records like this, how can I fix this:

select m.number, m.workphone as master_workphone, d.workphone as debtor_workphone

FROM master m

INNER JOIN debtors d ON d.number = m.number

where (d.workphone <> m.workphone)
AND NOT (d.workphone = '' AND m.workphone = '')
AND NOT ((d.workphone = '0' AND m.workphone = '') OR (d.workphone = '' AND m.workphone = '0'))