Bad experience from Netstar

Very bad experience. I bought my car in 2021 September, they installed their device which I was told will be a 3 year contract. I no longer have that car since 2024 June but have been paying until around April this year. I then decided not to pay any more because anyway we are no longer in contract since it was a 3 year one, so the 3rd year ended in 2024 September. Now I have been handed over, getting calls like crazy that I owe around R700. I asked them for a simple thing, a policy document as well as the statements from 2021. How do I owe when it should’ve run from a month to month because we no longer have a contract. Can you please intervene Hellopeter