Over billed on price lock

I signed up a for price lock contract a few months ago. I received the new Explora decoder. I was promised my dstv premium will be locked for 2 years, but I have been overbilled eversince. I have made numerous calls to the DSTV call center where my calls kept on being escalated depending on the Consultant that would be picking up my call. I'm tired of spending my airtime where I don't get better service in terms of my issue.