Cancellation fee of R999 - shocking

I downgraded my services in July 2024, the agent was kind enough to pass me a credit of R820 and downgrade me . To my surprise, the R820 was deducted for end of Aug . According to the agent Im speaking to, a downgrade was never done . I asked to cancel , now I’m asked to pay a cancellation fee of R999. I am a customer for over 3 years and due to affordability I wanted to downgrade . I provided my WhatsApp where the previous agent advised about the downgrade but not suffice . This is extremely poor service as a customer is providing proof of the downgrade but agent not trying to assist. If I don’t have the R820 where will I have R999 for cancellation. Disappointed