**** coverage and i must continue to pay for the contract of pay a large penalty

I took out a contract on a Huawei mobile wifi e5573 the online service said I had coverage well some coverage its so poor I have internet about 10 percent of the time and no email most of the time, I have now been fighting a war with facebook Telkom who tell me I am going to have to pay penalties if I cancel this contract. !!!! Why ????? This is not my fault you are the ones who say we have coverage but you don't bother to check that the coverage is going to be sufficient to run internet and emails and at a fast speed???? So I must pay for your muck up??? No way you get one of your managers to sort this out so I can take this back and get this cancelled with a refund for what I have already paid an no penalties why must I pay if you cant get the job done right