Promised credits have not been received

My promo plan expired so I switched to a new plan.  While chatting with the agent the chat was disconnected, another agent picked up the chat, apologized for the disconnect, and offered me a ten dollar credit which I thankfully accepted.  Thankfully I saved the chat transcript.  The agent stated my March bill would be 77.84 yet today119.00 was deducted so today I started a chat.  After three different agents I managed to get that cleared up.  Because I spent hours of my time fixing xfinity's mistake I requested a 30 dollar credit and the agent agreed.  The credit never materialized nor did the 10 dollar credit the previous agent promised.  The three agents I chatted with are Kunika, Rishabh, and Priyanshi.  All three agents ended the chat before the problem was resolved so I jumped thru the phone tree till I connected with a human being.  After explaining all of this to "Maria" she told me the agents falsely promised me those credits and there was nothing she or anyone else could do.  I have it in writing from xfinity employees that I would receive these credits yet Maria is telling me otherwise.  Why? Now I have been transferred to retentions and once again I'm being told there is nothing that can be done.  I have it in writing from three different agents that I would be receiving 40 dollars in credits.  This is fraud in my opinion.