If you asked for a quote after being told you needed treatment I'd think the insurance company would be very wary. Now you're well downstream from the treatment most companies would likely insure you.
We've recently got back from a month away and then got covid for 2 weeks. We take out annual cover as our trips tend to be several weeks and the difference with single trip isn't great. Although changing from European to Worldwide excluding USA ramped it up. I think my age, 76, has begun to tell as well. We paid £530 without baggage or travel disruption cover.
If prostate cover was very expensive I'd go without the prostate cover and perhaps go to single trip insurance.
Anyway your cover sounds very reasonable if it was basically free plus £112 with your bank account, no doubt you checked the small print. Regards Peter