Product: Bank account or service

I have a business checking account and associated line of credit ( LOC ) with Key Bank. I have enjoyed working with them for about a decade. At the same time they acquired XXXX ( this XXXX ) I sent {$6500.00} ( XXXX different transactions ) from my XXXX Bank account to my business checking account. After many calls and showing Key Bank the proof of deposit/receipt of the first installment ( {$3000.00} ) they finally agreed to credit my account with the money. I was then told that they also got my {$500.00} second installment, but they used it top pay late fees that would not have been there if they had correctly deposited the first installment. In a phone call they told me that they had cleared it all up ( but never sent me the details ). I sent in a third installment of {$3000.00}, having faith that they corrected their processes. The local Key Bank representative that told me all of the money was there and now accessible, but showed me no proof, no longer returns my phone calls or messages. The corporate customer service people have been very nice - as is their job - but they are unable to get me my XXXX Installment ( {$3000.00} ) or get me the details of what they did with the {$500.00} XXXX installment, other than telling me that they used it to pay fees I accumulated. I have the XXXX Bank checks of all of the deposits, complete with Key Bank 's stamped information on the back of the check. Customer service confirmed that they have received the proof, confirmed that there is at least {$3000.00} missing, and confirmed that I should not have had fees taken from the {$500.00} installment because it was their error. 
The intent was to deposit the funds into my Key Business account and then transfer the money to pay on the LOC. I 've been doing this for nearly 10 years. What is additionally odd is that when they found the first installment of {$3000.00} the did n't send it to the designated account number ( the checking account ) but sent it straight to the LOC. Then, they told me that the same thing happened with the {$500.00} I sent to the checking account ( complete with the checking account number on the cashed copy of the deposited check ) - it went to the LOC account instead of the checking. They had no explanation for this. The still missing third installment of {$3000.00} was also directed to be put into the checking account. 
This has gone on for about 2+ months. I have wasted at least XXXX between dealing with both XXXX Bank ( who Key Bank initially blamed ) and Key Bank. Key Bank ONLY stopped trying to discredit me and XXXX Bank after they received proof of the deposited checks. Now all they tell me is " We are still waiting for a response from up above. '' I want my entire deposit ( {$6500.00} ), the fees waived, interest being charged on the LOC to stop be corrected AND stop being collected during this time period - after all, the interest is for them doing their job as my bank, which is not happening - and I want compensated for the time I have been trying to correct their mistake. I am a XXXX and I lose money every single time I deal with this. 
I was using the LOC to pay quarterly taxes, which I can not do without access to the deposits I sent. Therefore, I am also going to be assessed late payment fees from the IRS. 
To Key Bank - I was a huge fan for many years. I even sent gifts to the local branch staff in XXXX ( such as chocolate covered fruit to say thank you for their continued great service ). I believe you can make this right, and I believe that you are going through a tough operational challenge, but you are stealing my money and that is called theft. If you can not resolve this to my satisfaction and the satisfaction of the law I will be required to hire an attorney and take you to court. I absolutely do n't want to do this, but it is your choice.