Alliance system error on settlement offer

Hi I would like to report a bad *********** service that I received from alliance,I was given a settlement offer of 2 months in November to settle my account amount: R2094 that was taken in 2 installments of R1047 November and December. A paid up letter was given to me after the last payment. They debited again and was told by their consultant to dispute that. Surprisingly enough I’m now sent emails and was called this morning was told that there was a system error I must pay more as the settlement does not apply anymore. Is that Lagan though why must I suffer for their error. Their calls are recorded they must go back to them and my Acc must be cleared cz I took an offer and it went accordingly