Where to raise complaint about courier?

Hello,

tl;dr:
Fedex have referred an invoice to a debt collection agency despite me waiting for their clearance team to respond to me for months, and I have followed up several times.

I bought some goods from China in January, $300 worth of electronics components that were shipped using Fedex. The website I bought them from had an offer of free shipping if you spent over $300. On the invoice it listed shipping as $150 and then discounted it after.

Before the goods even arrived, I emailed revenue with a copy of the invoice to ask what was the value I am liable for tax on, and they stated just the amount that I paid.

The goods were delivered in February , and in early March I got the Vat invoice, which charged the VAT on the full $450 amount.

• On March 12th. As per instructions on the invoice if I had a query, I emailed ieinvoicequery with my query. I received an automated reply with a ref number (lets say "x") saying my query would be answered soon.
• Fedex emailed me back on the 21st of April, answering only 1 of 2 parts of my query.
• I replied on the 22nd asking for an answer on the 2nd part.
• Fedex replied on the 28th of April, with instructions to get a corrected invoice from the vendor and to email ie-clearance@fedex.com using (my tracking number) as a reference
• I emailed ie-clearance on the 30th of April with the corrected invoice.
• On May 19th, still having received no response from ie-clearance, I received a final notice in post about this invoice. I had received at least one other invoice reminder by post prior to this, but as I was waiting on responses from Fedex around the query, I thought they may have just been an automated process.
• On May 20th I rang customer care line and was put through to the invoice department. I asked why I was receiving these notices when, as far as I was aware, the ball was in Fedex court. The person told me that there was no record of the invoice being queried , and that the "x" reference number I had been giving with the original email was not showing up. She opened a new query ("y") and said they would chase it up.
• On July 14th, still having heard nothing from Fedex, I was rang by a debt collection agency claiming to work on Fedex's behalf following up on an outstanding invoice.
• On July 14th I rang customer service again to ask what was going on. She seemed to mentioned I had been contacted via email on some date in June (I didn't catch the date, but I have received no correspondence from Fedex other than what is detailed here). She mentioned that they would inform the debt collection agency that it was being followed up on that she would follow up with ie-clearance. I offered to send the corrected invoice again, which I did after the call.

I still have no response from Fedex, I even followed up with an email yesterday detailing the case to date (basically these bullet points). I emailed it their invoice department, but decided I'd copy their main contact email too listed on their website "ie@fedex.com" which bounced.

I don't think this is acceptable by Fedex and I'm wondering where I can raise a complaint about it, as they seem incapable of sorting it out.

I can't keep wasting time chasing them up to try pay them money when they are not responding, all the while waiting for a debt collection agency to keep hassling me.

I do owe VAT on this order, and I'm happy to pay it but according to revenue they are charging me on the wrong amount.

I have wasted so much time on this already and I just want it over with. As a matter of principle, I'm not just going to cave and pay the initial amount, unless I am advised by revenue that their initial advice is incorrect.

Thanks for your advice