Surprise double insurance going to cost thousands

Hi everybody. I am a 24 year old and I have been going to physical therapy for a little over a month now thinking that I was on my dad’s insurance. I just found out today that my company auto enrolled me in March into a lousy health insurance plan (I did not fill out a form to waive insurance within the first couple months of employment), and that I will have to pay for all of the physical therapy out of pocket now (around $2,500) to meet the deductible of $4,000 (also the provider is out of network, so even when I have met the deductible I will still have to pay 30%). I called the insurance provider and they told me that they were unable to retroactively cancel insurance, and that I would have to talk to my companies HR and get them to cancel the insurance. The issue is, my companies HR has a strict policy that they do not retroactively cancel insurance unless there has been a life changing event, but in my case it seems I have not had a life changing event that meets the criteria. I was wondering if there is any other way for me to retroactively cancel this insurance plan so that I can put it on my dad’s insurance which is way better and the deductible is already paid off, and so that I can save a couple thousand $$$.