Telkoms been charging me for a 10mb line for Years

Hello<br> <br> Today I just found out that Telkom has only been supplying me a 4MB for years, roughly since 2008 which was upgraded to a 6mb about a year or two ago. Telkom told me that my area only supports 6mb. Today I've found out that I've been paying for a 10mb package for MONTHS if not years even though Telkom cant even deliver a 10mb service until last week since they upgraded the exchange year. When I inquired about upgrading my service it turned out that I've been paying for a bigger package that telkom cant even supply to my house! Why does telkom allow this? Overcharging me by over R200 for months, for something I cant even have?