Rejected Claim

I had an operation on 17 August 2017. Since then I've been trying to claim back for the procedure. In December '17 I was sent an email stating that my claim was rejected as I had a pre-existing condition and I was still in the "waiting period". This is completely inaccurate and untrue as the 2 year medical my doctor sent them clearly states this was NOT a pre-existing condition. Clearly someone on their side didn't bother reading my medical or they just don't care or are too lazy to do their job. I responded to the email saying that my condition was not pre-existing as this is the first time I've ever developed this condition. When I signed up for Oneplan I had a clear bill of health. I then received an email with an attachment referring me to a complaints policy if I'm not happy with the outcome. Why do I have to go through the unnecessary steps of complaining about my rejected claim when Oneplan has not read my medical and taken into consideration that my condition was not pre-existing as once again stated in medical. This is an error from Oneplan's side and they should be fixing it. My doctor has emailed them another letter stating that my condition was not pre-existing, she is also willing to phone and speak to someone. This is unacceptable and a waste of my time.