Bad service received from NMG!!!!!

I have been battling for 3 weeks to get my payment from NMG, their staff is VERY unfriendly and unhelpful they have processed my payment x2 now with the incorrect type, no one is taking responsiblity or contacting me to notify me of any erros / or phone me back when I leave messages!!!! I keep on phoning to follow up with them, and the person who need to assist me is not available or not in the office, the people I speak to lie and say they did forward my information to the correct person but when I question that person they say it's not the case? I need this issue resolved before month end!! How can it take 3 weeks just to authorise and make a payment? payment rejected now AGAIN!! because they have used the same incorrect type as the previous time?!