Dealing with mother in law's account

[#1]

Hello (hopefully DCT can respond to this)
I administer my mother in laws account for her. She is  currently on a 10GB/month limited product for £10 (high cost area). She now needs more capacity because she's discovered catch up tv. The only upgrade option for unlimited will double the cost to £20
I used the online chat system today, to see what can be done - because we could get BT unlimited for £8 per month - a massive difference. I was informed it is necessary to call the options team - either to find out what options are available, or to get a mac.
She knows nothing about the service, and will be unable to answer the most basic of questions. I also don't want any hard sell of inappropriate service.
Is it possible for me to make this call on her behalf. She is not local to me, so it will not be possible for us to be on the phone together. Can she for example raise a ticket to authorise this.
Thanks.

[#2]

She can indeed raise a ticket nominating you as an authorised representative

[#3]

Excellent - I'll have to help her do that of course. Thank goodness for remote control.

[#4]

I didn't say this
Just log in to your mothers account pretending that you are her and do it yourself assuming you have the account name and password

[#5]

Ask her to raise a ticket and post the ticket ID here so I can have a look at the authority issue for you.