Credit reporting or other personal consumer reports: Improper use of your report

In the summer of XXXX, on XX/XX/year> I contacted XXXX for a credit limit increase on my credit card. They went ahead and did that but did not warn me that they will be doing a HARD inquiry on my credit report. Had they told me so I would have NEVER asked for the increase. A while later I caught the mistake and called the bank to remove the inquiry. They admitted their mistake and they said they would send a letter to Experian to remove the erroneous inquiry. Needless to say I checked my report last week as I was thinking of getting a new credit product and notice that the inquiry was not removed. I contacted XXXX and Experian NUMEROUS times and both organizations have been giving me run around, telling me that the other organization is responsible and REFUSING to help me. I am fed up with their XXXX and need your help please!