Here is what's being counted as slavery from your source: Forms of modern slavery include slavery by "ownership" ("chattel" slavery), government conscription (forced military service or government labor), forced prison labor, forced migrant labor, debt bondage (slavery until debts are paid), sexual slavery, forced marriage/child marriage, child labor, and forced begging. With the definition of modern slavery in mind, we can now move on to examining the statistics.

Your 13,000,000 slave number is only chattel slavery. You're comparing apples and oranges to better make your point.