Unacceptable Service

I bought a New Mazda CX3 in 2020 from Mazda Midrand. The vehicle came with a 3 year maintenance plan. Last year as my maintenance plan expired/ended I asked the service advisor to extend my maintenance plan. She then said that it is not worth it as I would have to +-R15000-00, and that my services will cost me +-R2600 per year. So I decided not to take a extended plan. On Saturday the 10th of February 2024 I took my vehicle in for my annual service, only the get an invoice for more than R5000-00. When I asked and showed the huge difference in in prices of parts, I was told that the workshop gets discount prices. I then said to the service advisor that the difference is that last year it was a maintenance plan and this year it is due to the fact that I must pay. If I was informed correctly last year I would have strongly considered to extend my maintenance plan. I feel this is totally unacceptable