My contract was downgraded

I think i will be moving to another provider when my contracts end. One of my contracts with Vodacom was upgraded last year November 22 to 50GB Topup. I had no problem at all with this upgrade but this year February 23 a lady called me saying she is going to upgrade this contract as I am an old Vodacom customer (which I am) so that I pay less for more data. To my surprise at the end of February I found that the contract has been downgraded to 30GB Topup and I am paying more than before. I have written emails to Vodacom but they are not responding to my query. This is not the first time I am treated badly by Vodacom. Another contract was upgraded and the airtime that I had disappeared even though I did not change the sim card. I feel like Vodacom is robbing me even though I have been very loyal and have more than one contract with them. I will not be upgrading my contracts any more. I have to move and choose another service provider at the end of all the contracts I currently have with Vodacom.