AT&T Wireless Overcharging Nationwide

I once  I contacted them about getting unlimited data and lower rates on my account. I was paying $150 a month, after speaking to them and they said they would lower my bill the next bill came in at $275.  They did not give me a refund and told me it would work itself out. After a few months I transferred to consumer cellular and for some reason I was still being charge to AT&T and again they with fused to drop those charges of $86. The charges are ridiculous and I find that they do this to the elderly.