How can I escalate or make complain?

I recently purchased Macbook Pro from the UK during my visit, I wanted to purchase the macbook pro but with arabic keyboard which comes as a free upgrade. I head first to the Convent garden store to do my purchase but they told me the apple process has changed and upgraded items can only be purchased now from the online store. I asked for the VAT refund and I was told online store is the same as the retail store and they can provide me with the same services.

so I made my purchase online and once the Macbook pro delivered, I contacted the customer support to ask for the VAT refund invoice, the advisor called me back and gave me the procedure to do the return which I written down, She asked me to print the invoice they sent me and take it with me to airport VAT refund office for stamp and then once I reach my destination abroad I send that stamped invoice with prof of residency and ID to apple for them to process the refund.

I went to airport but the officer refused to stamp the invoice as it was not VAT refund invoice! she stamped my other VAT refund invoices but she told me I was misadvised by apple and that they should provided me with VAT refund invoice for stamping.

Now I reached my destination and I am contacting the apple store to advise me what to do, but they change their account and they are saying they can only process if there is fright shipment invoice, this was not the advise I was given in store or in the phone when I spoke to them(I believe the call is recorded).

Few email exchange, I keep asking to be provided with complain & escalation procedure under UK consumer protection Act, and they ignoring completely answering this question and instead repeat the same answer and without any apology or reference to the phone call I had with their advisor.

I could not find any complain procedures or number I can contact on apple website, which is very strange and I am not sure how legal is this in the UK.

Can anyone help me with number or email to address my complain please?