Technical issue with payment

I recently sold through Payfast, everything was going as it should be the buyer send the money to them I the seller would send the item once the item arrives at the buyers address they would release the funds into my Payfast account but they made a ***** up with the payment. Instead of release the original amount R3800 into my account they deducted an additional amount of R2300 from the buyer 's account making it R6100 they took from the buyer, they advised the buyer there is no way to reverse that but now they want me to send them R2300 then they will release the full amount of R6100 into my Payfast account. I informed them that I don't have R2300 to send them but now they are keeping my funds R3800 because of there technical issue that happened.