Taminisha,
Sorry to hear that your family visa has been rejected. If they have already asked you to come after 6 months then there is nothing "Legally" you can do about it.
If you are sure that you had all the valid documents (Verified and Stamped) from all authorities in your country and by MOFA in Qatar, then I would suggest you to either wait 6 months or approach a typing center (Visa Agents).
Family visa depends on many criteria:
1- Your salary
2- Your visa category
3- Your certificates
4- Your residence documents
5- And who you are applying for