Thanks for your post and apologies to hear your mums bill hasn't changed much despite removing elements of it.
Goslow, our VIP, is spot on here. We're not able to give you a standard pricing as once it's added on to your package with TV and Broadband, there are discounts added so you never actually pay full price unless it's the only service you have.
As the call charges are mounting up, it is worth speaking to the team on 150 / 0345 454 1111 and asking them for information on how much it would be to add back on to the package. This will likely save your mum some money going forward due to the call charges you've already mentioned.
Let us know how the call goes and if you need anything else, you know where we are.