I'm no maths expert but it think your calculations are way off.
Why add R value to % and then get a total in %?
Lets take your R100, they charge 2.75% + R2.50.
2.75%*100 = R2.75 + R2.50 = R5.25
You would be paying them R5.25 per R100 transaction.
R1,000,000 on a single transaction...