Ok , point taken, but I know full well I am being charged 19.99 per month for line rental( or was) and that (was) the exact going rate ( less the discount for advance payment) for a landline only contract( now £23.05) so, my aim is to reduce the package cost by a good chunk of that £23.05 whatever it is called.
When you ring BT make sure that you know what other ISPs are offering. Fibre 2 is £38.99 for new BT customers - I don't know how much more Halo is.
I personally would only talk about the contract pricing and would seriously not bring anything about line rental into the conversation. Your sole aim is to reduce the £50.87 you are paying to a sensible figure which may be £43.
You also need to be aware that you will be re-contracting so your current package may not be available. You do not need to immediately accept anything but can ring back another time as you could be offered a better deal - it's a bit hit and miss.
There is no need to do anything about the calling plan as it is effectively on a rolling monthly contract.