They talked me into their phone service. The service was poor and they billed more than advertised. Quit their phone service after 5 months but still had billing problems. I always paid what I agreed to but billing was always off. After months of trying to work out with long phone calls, they agreed to a fair credit for past billing errors. A month later the billing was still wrong. I called again and they indicated they changes their mind and removed the credit. Can they do that?