No value for money as per contract promise

I took Neo Flex Data contract 10G in February 2015 from Neotel. I received a poor signal and an aerial was installed after about three e-mails complaining. Thereafter the problem persisted so I was told to move the router around. For March, April and May I used less than 50-60% of the 10G data per month. in July I received an account of R548 because I was charged out of bundle. I paid and had a cost cap. Thereafter the data was depleted in the 1st 5-10 days of the month. I sent numerous e-mail but no explanation could be given except to advise that I only switch on when using data. This did not help ,it just got worse.I informed them on 30 Nov 2015 that they could not resolve my problem so I ended the contract. On the 9 Dec 2015 I was called by a staff member who did not listen to my explanation and clearly did not read any of the e-mails sent . I was instead told that I must pay a penalty of R1649.91for the bad service received .I also informed them to collect their router . This account includes the cost for data over and above the R176 . I have to date received the standard responses from call centre staff . I am at wits end with Neotel.