internet connection bad

Yesterday I called mtn customer service and complained about the very ridiculously slow throttle I'm getting when trying to download, I explained it's so slow it times out and then takes me to the webpage saying I have ran out of data and airtime when I actually had 1Gb of data that mtn sent for some 3Gpromo. The agent said it's coz every mtn customer received that 1gb data and they're using it so it would be slow but when I use my own data it would back to normal well it's not back to normal I bought a 250 mb data and after 3 hours of trying to contact them coz I had no internet connectivity at all, I finally had connection but I'm still receiving the I have no data and airtime **** when I still have 250mb data that only expires at 6am. This is poor service and unacceptable and this ain't the first time my data went wasted but now I'm just fedup. Please resolve this issue immediately. I'm using ***