How is this legal?

Shocked and disgusted. I shipped a package in from America using MyUS's services. MyUS made the mistake of listing the value of the package as more than double its actual value ($924.99 instead of $419.98) even though I submitted the invoice from Amazon before the package was even logged. I notified them immediately of the problem before the package was even marked for shipping. Eventually they rectified their mistake and paid me the erroneous overcharged amount for insurance and insured me that they will notify FedEx of the problem so that they don't charge me incorrectly for import taxes.

Shortly afterwards I had a phone call with a FedEx employee (Innocentia Sithebe) and notified her on the call about the error and afterwards I sent her an email with the original invoice as proof of the actual value of the package. (This was before the package even left America). I have the emails as proof.

A week later I got an invoice from FedEx to pay more than double the VAT that I should be paying and listed the incorrect value of the package $924.99 (Instead of $419.98). I responded immediately notifying them that they made a mistake and forwarded them the email correspondence that I had with both MyUS and FedEx to notify them of the problem far in advance, but FedEx (Vanessa Christine Vorster) told me that customs cannot accept a second entry and FedEx will not be taking responsibility for the mistake even though I forwarded them all the proof that I did everything in my power to notify them far in advance.

I am honestly lost for words. I did everything in my power to try and fix other people's mistakes as soon as possible, but still they just bulldoze over you and refuse to take responsibility for their mistakes. I wish I was in a better financial position to do something about this in a court of law.