Messed up my credit report, do I need to hire a consultant to fix this up?

[Expert]

This 7 years period starts from the date we took loan or defaulted on the payment of the loan?

The seven-year clock typically starts 180 days after the account first went delinquent (or defaulted on the payment). Check your credit report, it will show you the date, your bank reported to the CIBIL.