Telkom's *****-up is now my problem

I signed up for a 24 months contract in Oct 2022, when i checked to see when my upgrade date was don't i discover it is only in Oct 2025. I went to the store I initially opened the contract only to discover that is was captured as a 36 months contract. After many trips up & down to the store I eventually get a call from the billing department apologising for the error on their part but I must still pay for the remaining months but at a reduced amount of R70 (for the device only as she stated). Why should I have to pay for their incompetence, an error made on their side is now my problem and expense. This is shocking service. A "sorry" from an agent does not make up for the extra amount of money I must pop out for an additional year when my contract was supposed to end this year Oct 2024.