I would just stop the direct debit and to hell with it. Whats the worst that could happen ? They will phone up and ask for the money , your daughter will answer the phone to be told that a new D D needs to be set up to continue the contract , she can either sign up from her own bank or lose the phone.
The worst that can happen to you is an entry on your credit record saying you have not compleated a contract. You will get letters asking for the money but just bin them , do not respond and they stop bothering after a while.
You have been too soft with her time for some 'Tough Love' she is really taking the p*ss.
I have 5 children ( 26 to 38) and am now 62 and retired, I have to be very firm with them now and refuse such requests , the 'Bank of Mum and Dad' has to close sometime .