Abnormally high cancellation fees for activation

I was with home-connect for 9 months before cancelling service. They charged me a cancelation fee for service activation for remaining 3 months which was almost equal to 3 months of payment. I had a previous fiber installation all I did was connect to home-connect ISP and now I am charged abnormally high cancelation fee. I lost alot of money and whenever I contact them they just tell me I must pay and cannot explain why so high fee.