Mnt suspending lines when already paid.

Made a cash deposit into Mtn account on April 8. Sent 2 e-mails with pop.Phoned numerous times, they remove the suspension but then suspend the lines again,( 4 times). Now we are grey listed.!Receiving sms about bad credit! Can someone just do their job! We did pay and sent the proof!!!! What more must we do for heavens sakes???