Telkom Online Sales- the customer is expected to pay for a mistake made by them

Telkom Online sales incorrectly captured my order, apparently they had two promotions running and when they were capturing my order, they mistakenly captured my order incorrectly. - I called Telkom the day after receiving my device, I was informed the issue was being escalated. - There has been a back and forth since trying to resolve the matter, today I received an email telling me that the cannot resolve my matter. - I have proof of what I app**** for, I have call register of the days I have been calling (apparently all calls are recorded). - Today I am told that they cannot assist me, the agent who assisted me with the application is only receiving my complaint today. - I cannot even return the phone because the cooling off period has passed - The mistake is on their side, however, I am the one who has to suffer all the consequences. - A big company like Telkom, is unable to rectify a mistake which happened on their side. They are expecting me let accept their mistake and let it go.