Xfinity Not Honoring Promotion

As stated by numerous Xfinity users, I purchased a new phone during a promotion. I added a new line of service with premium unlimited. The promotion was $400 the phone spread out over the 2 year financing period. When trying to place the order initially online, the credit wasn't appearing. I decided to reach out to a chat agent to verify the promotion would be added. They helped me place the order confirming the credit would appear as soon as I received the phone and activating it. After receiving my first bill, the credit was not applied. I thought this was maybe because I activated the phone a week or so after receiving it and maybe the bill had already been processed before I activated it so the credit wasn't reflected. I reached out to customer service and was informed there was no promotion added to my account. I asked them to refer to my previous chat (because we have no way of submitting evidence of transactions, and even if we could, the transcripts fail to download every song time). They told me they could see where the agent forgot to add the promotion, but they couldn't do anything about it. They offered me a ONE TIME discount of $30. I reached out again when my next billing cycle came up. This time I was told the couldn't look at previous chats but offered me a $40 credit. I told the agent I wanted this billing issue resolved. I didn't want to have to reach out every month. I was told there was nothing that could be done. I asked to speak to a manager/supervisor who would have access to fix this. After waiting roughly 30 minutes I was put in contact with a manager. After explaining the situation, they told me there was no promotion on my account and the full bill would be due. I explained again that this was the whole issue I was trying to resolve. The "solution" offered was to give me a $30 credit (so $10 lower than the person who transferred me) and to reach out every single month to get it credited. I told the agent this was unacceptable. If I have to reach out every single month for 23 more months I wanted a larger credit than what I originally signed up for. Upon receiving my message the representative credited my account, and ended the chat, transferring me to INTERNET who had no way of helping me. This has taken several hours of my time for something Xfinity messed up on and refuses to fix. After researching this more, it appears to be a very common problem with Xfinity. I'm at the point where I want to cancel all my services and go somewhere else where they aren't so shady with everything.