No response nor resolution on problem caused by Fedex

In September I used Fedex's services to deliver a cellphone from the UK to my sister in Cape Town. Unfortunately Fedex's agent in the UK underestimated the value of the phone by R300.00 on the waybill. The fee the for Fedex service was R 1500.00. On 27.09.2017 Fedex informed me that the phone had been precleared and will be released on payment of a further R585.00 which I promptly paid. However the phone got stuck in customs and I was informed by Fedex that a penality of R289.00 is required to release the phone. This has since increased to R 1200.00 and I have two weeks ago requested for this to revised due to a mistake not made be me. I am quite willing to pay the penalty but not the excessive Fedex fee. Despite of more than 25 e-mails to Fedex this matter has not been resolved.