It could be CFD if you are a long-term investor.
Say you buy a CFD contract with 50% margin @ 6.5% + 3% = 9.5%
Because your account will be debited every day the interest rate is not 9.5% but more like 10.5% AND over the whole position, so you are paying 21% p.a. right there over the money you are really borrowing.
Suppose your position doubles in value over a year, which is not uncommon, you again pay interest over the value of the position and your interest rate is now 42% over the borrowed part of your position.