Super bad service on customs clearing

One of my worst experiences with a courier company in more than 15 years. It took them 4 days to send me an invoice for custom clearance . I paid within 10 minutes and send POP, and they simply tell me I have to wait another day for the payment to show in their account before processing/clearing will happen.

Sending email to there customer care - the email was deleted without reading it

Log a complaint on the website - the response was that the shipment is undergoing clearing at customs which is simple not true as there was no invoice to be paid for customs clearance. Case was closed on the website with no resolution to the problem.

After many emails and many phone calls I managed to speak to a team leader who said she will upload for clearing - time will tell if this is happening

For a company that has "lightning fast delivery worldwide" - 4 to 5 days for clearing at customs ??????? - I am not sure if I can agree on this