But it's not the diabetes that is the problem since you had the required coverage for the scheduled trip - it's a consequence of the delay, which should surely be covered by the insurance ...?
I would just let them know that you are keeping a diary of your requests for test strips and their rejections, and will present the evidence should you ever get admitted for complications (retinopathy, neuropathy, leg ulcers etc.)
If they change their minds, thank them profusely - positive...