First, you mean voicemail, not answerphone. (That used to be the trademarked Bell System name for their telephone answering machine.)
Second, Vodaphone would almost certainly help, since it's their voicemail system. But you can do it yourself. Fisrt, figure out how long you'd like, in seconds, before the call goes to voicemail. (It works by time, not number of rings. Since rings are 1 every 5 seconds, figure 5 seconds per ring, then add 2 [you and the caller don't hear the rings at the same time].) Call your voicemail, listen to the prompts (it may be in "More" or whatever they say for the extended menu), and reset the time before voicemail answers.
If you can't find it, call customer service and ask if they could please set your voicemail to pic up after <whatever time you decided> seconds. They get these requests all day long (usually without the please", so hearing one would brighten their day).