Product: Credit card or prepaid card

XX/XX/XXXX, Capital One gave me an introductory 18-mo. 0 % APR rate on its credit card. 
XXXX  XXXX : I knew the end of the promotional period was coming up, but the end date was not on my statement. Meanwhile, I made all minimum payments on time. 
First call, XX/XX/XXXX, XXXX XXXX  : I called Capital One re. the end date of the 0 % APR. I was told that the introductory APR had actually ended on XX/XX/XXXX. 

Second call, XX/XX/XXXX, XXXX XXXX, I contacted Capital One to ask them the date by which I needed to pay off the entire card balance, so as to not incur -- or at least minimize -- any interest. 
The agent told me that as long as I paid the minimum payment on time every month, that I would incur no interest. 
I knew that I now had an APR, and that this could not be true. 
I tried to tell this agent that I no longer had a 0 % APR -- but that now I had an ~ 25 % APR. 
My efforts for clarification made no difference : This agent kept repeating this error, as if reading a script ( e.g., that making only the min. payment was ok ). He did not seem to have my APR info on hand. 
I gave up trying to communicate with this agent, & ended the call politely. I called again, hoping to get someone knowledgeable. 

3rd call, XX/XX/XXXX, XXXX XXXX  : I called again. The 3rd agent sounded more knowledgeable than her predecessor. 
This agent confirmed that my 0 % APR had ended on XX/XX/XXXX. 
But that I should not worry about interest, because my billing cycle had not yet ended. 
The agent told me that if I paid off the entire balance by the end of the billing cycle ( XX/XX/XXXX ), that I would incur no interest whatsoever. 
I went over this piece of information several times, repeating this info back to the agent, to ensure I understood correctly. 
I also told this agent about my prior call with her less-experienced colleague. ( E.g., the agent who had erroneously told me that making the min. payment would incur {$0.00} interest. ) I stated that such an error could potentially cause great problems for customers, & that Capital One should be more careful re. its training of new employees. 
This agent agreed, thanked me for alerting her, & said she would make a note of the erroneous prior info. 

XX/XX/XXXX : I paid off my full balance ( {$7900.00} ). I thought everything was ok. 

XX/XX/XXXX : My new statement showed an interest charge of {$150.00}. 

XX/XX/XXXX : I called re. this charge. 
A different agent told me that the information I had had, was incorrect : That I now owed interest going back to XX/XX/XXXX -- and that of course new interest was accruing every day. 

I explained that I had Capital One had itself given me incorrect information. And that I had repeatedly gone over this information with the agent at the time. And that Capital One would have a recording of these conversations. 

In light of Capital One 's own error, I requested that Capital One waive this interest ( the first few of any kind they had charged ). 
This agent said there was nothing she could do to waive the interest. She said that she was sorry for the " miscommunication '' -- but that I now owed the interest. 

I acted in good faith. 
Capital One should : 1 ) include the end dates of promotional APR 's on its statements 2 ) Train its employees properly. 
3 ) Take responsibility for giving erroneous information -- especially on twXXXX separate occasions.