Change of surname on billing documents

I requested call center agents at Century City 3 times and also had telephonic conversations with the call center more than once, to change my surname to my married name. It is still not done. They made copies of my ID, marriage certificate etc and told me that it would reflect the next month, but that was a few month's back. A call center assistant who phoned me on one occasion after I complained, screamed at me and told me that it has been changed. Apparently it was changed on the system, but it doesn't go through to the Invoices. It still reflects my previous surname. Every time someone phones me back, they click somewhere else on their systems and promises me that it will be rectified, but I will only be able to see it the next month. They were able to change my address, but not my surname. The invoices from Cell is my only Fica document, I don't want to open accounts elsewhere just because they don't know how to change information of customers on their systems.