First -time poster needs help re Phone security/queries

[#1]

Hi All, sorry if the thread heading is a little vague. In simple terms there are two things I need help omn.
Firstly my itemised billing shows a day of premium calls made to what looks like porn/adult sites. We are 90% sure they were not made from the home and it is both worrying and confusing. Does anyone have a Plusnet contact number that might help.
secondly. My friend, whose phone it wants to do all she can to avoid unwanted use of her phone, I realise she can use a pin to lock her hand held phone, but of course if another phone where plugged in it would still be a problem. is it possible to do a more secure locking, of say the actual line.
am really a novice in all this technology stuff! so apologies if its all a tad more obvious than i imagine. Many thanks

[#2]

With respect to the second point is there only one phone socket in the property or are there several. If several is the phone normally plugged into the master socket (the one where the line comes into the house
I know BT offer this facility http://www2.bt.com/static/i/microsite/help_and_tips/faults/troubleshooting/barring.html http://www.productsandservices.bt.com/consumerProducts/displayTopic.do?topicId=25504 but as far as I know Plusnet don't
It is however a bit messy to use as it appears that you would need to remove call barring before making a call and then reimpose it

[#3]

Following Contact Us link from Plusnet site
"Residential Support 0800 432 0200 or 0345 140 0200 All day, every day
You'll need your username and password handy"
http://www.plus.net/support/customer_service/contact_us/contact_details.shtml
Premium Rate call barring can be arranged but costs £2.50pm paid in advance (less if bundled with other Call Features).

[#4]

Thanks so much for your replies guys, appreciated