Incorrect Tax amount required

Hope you can help, my father Mike Hervey was told to pay TAX on R750 000 income from Old Mutual (Unit Trusts for Hulkngi)) and he only received R630 000 which he is prepared to pay tax on. He has been advised to contact you but his email is not working (he lives in Natures Valley). Old Mutual is just passing the buck and his Financial Adviser has advised he contact you for some action. I will give you his phone number as not really sure of the finer details, many thanks Annabel Andrews