Overcharge on Afrihost account for service not rendered

I'm a client of Afrihost for the past few years. During the lockdown, I've upgraded my service to a 10Mbps line under the impression that my line speed will improve. After several months of poor line speed, I've contacted Afrihost to investigate why I'm not getting the line speed that I'm paying for. Afrihost informed me that my Telkom line, DSL can only run on 4mbps. For nearly 7 months Afrihost deducted money from my bank account for a 10mbps line and I only received 4mbps. Why haven't they informed me in April 2020 that I can't sign up for a 10mbps line as my Telkom line can only give 4mbps.