Flawed payment system and service from FedEx

I have had this issue on multiple occasions, but this is the last time I will ever use FedEx for my deliveries. You cant get hold of any agent via phone and the do not reply to emails. Ive had a package come in, subject to customs clearance. Ive paid the fee via the OZOW web app and a EFT and mailed the proof of payment to ***. Still I get mails telling me if I do not pay my package will be sent back or destroyed. Its unacceptable, not only will I loose my package, but I am also out the custom fees. Its ******** how inefficient and unhelpful they are