My ********** and ongoing nightmare with DHL

I sent my musical instrument (an oboe) to be repaired (under warranty) back to the manufacturer in London, however I have had endless delays in getting it returned to me, even though I paid for an expensive courier service. I am a professional musician so this is my livelihood and therefore incredibly important. I chase up DHL several times a day with telephone calls and emails and have been given misinformation and poor service at every turn. Each day when I call I am asked to provide new documentation, or I am told about new complication. Each time I solve the issue by promptly providing the requested documentation or information, I check with the members of DHL staff that I have now provided everything that is required of me. Each time, they tell me that I have. When I call later or the following day to check on the progress of my delivery I am told that I have not provided the necessary documentation and that something new is required of me. Members of DHL staff regularly promise to call me back by the next morning but most of the time they do not bother to do this. During one conversation I asked to speak to the manager but was simply told that they were busy and would call me back. They never did. I am travelling to the UK on Friday and it is imperative that I am able to take my oboe with me. The whole purpose of this expensive trip is to play it. I am suffering from sleeplessness and anxiety now as a result of this situation. During my last telephone call, it seems that DHL have now released my package to Customs. However, given the terrible service and misinformation I have so far received, I do not trust DHL to submit the proper documentation in a timely manner to Customs and fear further delays. I am so disappointed with the service I have received and will never use DHL. Furthermore, I will let all of my friends and family know that they should also never use this terrible company.