I’ve had plenty of nuisance calls from 07 3606 0825, although they have not asked for money, as there is no one on the line. You answer it and a few seconds later they (or the calling machine) hang up. If you call back there is a recorded message saying it is a charity organisation, but it doesn’t say which one.
Normally I don’t hear from them for many months, then get 2 calls per day for a few days, then they go quiet again.
Checking online, a lot of other people have had the same experience with this number. Unfortunatley there is no call blocking with Android 5 on my phone, but a previous version did have it.
I installed a highly rated call blocker, but removed it shortly afterwards, as it crashed every time I tried to run it, and haven’t bothered to try any others, as the calls have stopped again, for now anyway.