Tired & Disgusted

I was upgraded in March by MTN. The agent who assisted me promised & gave a gaurantee that my monthly subscription will be R299 per month on a topup package. I upgraded only my sim package as my handset is still in a good condition. I then received my April statement which required me to pay 4 hundred & some odd rand, I though to myself it maybe includes pro-rata or something like that. To my surprise the May statement came & I had to pay R408.07. I called MTN on 23 May & spoke to Mfundo Mthethwa who promised to log query & would get back to me in 3 working days with reference number ********** 95. 7 Working days later there was no response, I then called MTN back to speak to Thulisile Zuma. She gave excuses that she couldn't see the response email as Mfundo sent it from his personal email and Mfundo is not at work on that day. I then requested to speak to the manager. Thulisile kept me waiting for almost 20 min & eventually call got cut. I made a call again today 7 June & spoke to Matshepo Sehoshe. she advised that Mfundo hasn't received feedback as I was upgraded by summer mobile. I once more requested to speak to Mfundo's manager whom apparently was busy. I was then transfered to a manager called Marvin Pillay who gave me a whole new story. The "manager" told me to call another summer mobile number ********** 999 to get quick feedback. My question to him was: I'm contracted to MTN & have been for more than 20 years and expecting excellent service, instead I've been sent from pillar to post & have been promised feedback which I haven't received. Is this the service I should be getting every time I upgrade from MTN. I'm very disgusted by the service & think it's time to port to a service provider who values their clients