Agreed contract not been honoured

Hi there I wonder if any of the forum would be able to help me.

My elderly and not keeping to well mum was recently coming to the end of her contract and at the end of September agreed a new contract including 125mb Broadband and Mixit TV on her existing Tivo box for £26 a month for 24 months contract going up £3.50 each April.

The addition of her phone number was going to make it more expensive and she agreed on the call that she would port her number out to a new provider just to retain her number and forward it to her mobile.

The number was ported out before the agreed start of contract on 24th October but the initial bill was much higher but looking at it we thought that it would bounce back and mean she would not have to pay anything for a few months at least. The next bill has now been generated and she is being charged even more with no credit.

The agents on chat have explained that it is a known issue in the back end as the port which was agreed at the time, has put a stop to the contract but it should be easily fixed.
Despite this it has not been fixed and even as a last resort has put in her notice to leave in hope that this would trigger someone to contact her and sort out the mess.

This has also not happened.

It is causing her a great deal of stress and would politely ask if someone can contact me so that we can arrange some dialog with someone who can actually help without the constant back and forth and changes of prices she keeps getting offered which are now much more in cost for even less.

Thank you in advance

Please help