RIP-OFF and ********** Behaviour

My account is being charged interest which is against the contract i signed with TFG. the balance owing on my account was transferred to 18 months plan which attracts monthly interest without my consent or explanation in July 2017. I used my account to purche an item in Oct 2017 and that purchase was put on a 12 months plan without my consent again. I always request a 6 months plan when i purchase but I have just learnt today that since my account was once in arrears. I am now officailly charged interest even when I purchase on a 6 months plan. this is a huge rip-off and close to *****elent activity. if terms have changed on my account I shoulb be notified and i was never notified of this. And they are prepared to offer 1 month reversal on interest which is totally unaccepable to me!!! i want all this interest reversed as i never gave anyone consent to action these changes and my account tp stay interest free. this action amounts to debt slavery and i will be reporting this behaviour to the NCC. this must be investigated at a national scale as i believe this is not the first time you have done this