I have taken a data only contract with MTN and discovered that network coverage at my residence is none existant

I have taken a data only contract with MTN and discovered that network coverage at my residence is none existant. MTN provided me with an aerial and the coverage was a touch and go kinda vibes. But in all other areas MTN especially in town MTN coverage was excellent and got used to using MTN at work and Vodacom at home. But in recent times MTN network coverage is but everywhere I go and I reported this without any assistance. Now I tell them to cancel the agreement because they can't keep their end of agreement they say I must pay cancellation fee. Why should I be charged for their failure to provide me with a working network. I think they should be paying for all the forfeited data that was as a result of their failure to provide me with network coverage everywhere I go.