Vodafone — Why should I liable to pay unnecessary element added by service provider with bill

Myself Piu Roy Chowdhury, my mother Mrs. Swapna Roy Chowdhury, contact number [protected]. Her plan is Rs.399 and including GST, the bill amount is 471/- per month and payment (471/-) done by me without any fail. Being a senior citizen, she only utilise her phone for call receive and net shuffle.
But, in the month of Jun’23 video call charges & from Mar’23 onward, late fees charges add with her bill which was not paid by me. Not possible for me to check each and every bill, so, paid only amount of Rs.471/-.
Now, the the bill amount comes to (bill of Aug’23) Rs.1218.7.
On 11th Sept’23, after the payment of Rs.607/-, received a mail of 0(Zero) outstanding.
After 7 years, I ported my no. to another service provider(15th Sept'23), only because of these unwanted elements every time added with bills.
They asking for payment for those and telling that "the waiver given to you only for retention with Vodafone"(mailed on 21st Sept'23), this precondition was not disclosed by their customer care service at the time of waive off.
From 14th Oct'23, another service provider temporarily suspended my mothers no([protected]).
My question is that why should i pay unnecessary element added by service provider.