MTN is useless!!!

So i went into a contract with MTN for a 100gb day and 100gb night package. But i never received the full 100 Gb night. I brought it to the attention 3 times and no effort was made to fix this problem. Then i attempted to cancel the contract due to MTN breaking the terms of said contract and was expected to pay a massive early cancellation fee which i refused to do. Now MTN is taking a debit order for the remaining moneys owed on the contract. Am i wrong in being extremely upset with MTN, just because they a big company they feel like they can do what ever they want. Their signal in my area has gone from average to plane horrible but i am still expected to pay for a service that was not rendered.