Claim submitted a while back; no reimbur*****t yet

I submitted a claim and the service provider failed to include ICD codes. The provider amended the paid invoice and submitted the claim on Monday night. It is now the 4th working day, and this claim has not been processed and our monies not reimbursed. Why is that? Why do we need to keep following up? This is almost R1000 out of our pockets we are waiting to get back from Discovery.