"Wasn't given proper diagnosis/management or follow..."

I attended A&E at St Thomas on Saturday 19th July immediately after sustaining a sports injury to my left knee that morning. I explained to the healthcare professional that I saw that my knee had twisted and collapsed under me whilst playing sport, I heard a loud popping sound, there was immense pain and I was now struggling to walk. I indicated that my knee felt very unstable and I felt something wasn't right. After a lengthy wait, I was assessed by the healthcare professional I was told (in a somewhat condescending tone) that my knee was 'completely fine', 'all ligaments are intact and nothing is ruptured' and that there was 'absolutely nothing wring with my knee'. The healthcare professional advised me to relax, put on a brave face, go home and ice my knee and take painkillers as required. I was not referred on for any further review and I was not advised to seek any further medical advice - I was assured there was nothing wrong with my knee at all and told to leave. I felt as if I had wasted her time. The following week I went to my GP for a second opinion as I did not feel I had obtained accurate diagnosis from A&E and was still in a lot of pain. The GP referred me to a knee clinic who subsequently ordered a MRI. The results of the MRI are that my ACL is fully ruptured as a result of this injury - I am now awaiting ACL reconstruction surgery. This is in huge contrast to the advice received from the A&E healthcare professional who assured me my knee was absolutely fine. I understand that mistakes can be made and diagnosis isn't always easy, but I was disappointed that after waiting 3 hours at A&E, I was told to be braver, take paracetamol and advised in no uncertain terms that there was absolutely nothing structurally wrong with my knee (which is not at all the case). I was not referred for any further assessment or advised to take any further action and was told to go home. Quite frankly, visiting A&E immediately after my injury was a complete waste of time and I don't feel I was given proper management/advice/referral for my injury.