Mweb.. i Pay for 4MBPS ADSL but are only on 2MBPS

In Aug 2014 I upgraded my ADSL line speed from 2MBPS to 4MBPS. Mweb confirmed all is done and I started to pay for new line speed. I then checked on Telkom ADSL speed checker and according to them I am still on 2MBPS speed. I have send a email to Mweb also send a print screen from report. They then said that Telkom did not update the system yet. I believed them. I then checked the line speed again in Sept 2015 only to find that it still shows 2MBPS speed. Again I logged a call with Mweb, for a week I had no feedback. when I called they then said they discovered that the line jumped back to 2MBPS and they will log a call with Telkom. Telkom called me only to tell me that the speed is still on 2MBPS and was never changed. they will come back to me. I have send a email again to mweb with all emails attached asking what is going on and if I will get a credit for the line speed paid for but not received. again no reply. Must I maybe take it legal??? Mweb is *****ing. I have been a Mweb customer for over 10 Years??