I'm not overly familiar with the Pru products at all, never mind this one, but there are various documents online, giving information.
It looks like it is covered under the more comprehensive policy, which you don't think you have? Did you also realise they "only" pay 15% of the sum assured on diagnosis, so not the full amount?
I wouldn't get overly excited about then asking for a medical report. That is probably requested automatically, when a claim form is lodged. The people in the call centre, or on the help desk aren't usually empowered to make judgements on whether a form should be sent or not. If you call asking about a claim, they will send a form, so that you can then provide the correct information, in a formal way. These huge companies are incredibly inefficient at times, so don't build your hopes up too high. On the upside, it may be their polo to try to ensure they are not missing any other reason they should be honouring a claim by you - like for waiver of premium, or something. These days, it's much harder for life houses to quickly wash their hands of potential claims. There have been a few (very expensive) court cases in recent times.
See the process through, but don't go spending the money before anything is agreed!!
Good luck, and let us know how you get on.