I have both a PAYG and contract mobile with you. I always turn off the voicemail when abroad, as I've been caught in the past with charges caused by cold callers hitting the voicemail. On the PAYG mobile account, under Plans and devices, there are a number of options including turning off voicemail. This used to be the case for the contract phone, but now the only options that appear relate to parental controls and data roaming. Has this changed, or is there an error in my account?
Sorry, I missed out the heading Manage Your Services from my original post; as you say, these options should be there, but all I get is Parental Control and Going Abroad. On my PAYG account there's a full range of options! I suspect there is an IT issue with my contract phone account, so I'll wait for a VM response. Meantime I've tried those numbers you suggested in the past, and they don't work on my phone (Experia M2) for some reason.
Thanks for bringing this to my attention. I'm really sorry there isn't an option to turn off voicemail for your contract phone on your online account. This is quite strange.
I've checked my personal account and the voicemail option is there. I'll now send you a private message to see if I can find out the reason why yours isn't. To view this click on the purple envelope on the top right.