It sounds like you are stuck working with a "tough guy" from the collections dept. right now. Fortunately, you do have some options.
First, you may be eligible for an "offer in compromise". This is essentially a program where you make a reasonable offer to the Dept. in order to resolve the open liability. If handled properly, it is a win-win for both parties: The Dept. collects some revenue and the taxpayer clears the liability. Your first step for this route is to review the following publication to see if your facts and circumstances meet the requirements for the program. you can find this information here:
As you mentioned, it appears that you have some documentation in the form of register receipts which you can use as support to lower your liability from the estimated $155K. Such documentation is vital to negotiating a reduction with the Dept. In addition, you may want to consider requesting an abatement of the penalty charges assessed due to reasonable cause. In many cases, taxpayers without any prior issues can easily receive a waiver of said penalty.
In addition, contrary to what the collections representative said, you do have some rights, including rights to payment via an installment plan. You can find information on your rights and installment payment plans here:
Based on the information you have provided, it appears that you want to work with the Dept. to get this issue resolved. This is an excellent first step in reaching a resolution with the Dept. As detailed in the above publications, you do have options to do so in a fair and efficient manner. Your best bet at this point it to review the above information and let your contact know you are aware of your rights. At that point, he/she should either work with you to reach a settlement plan or put you in touch with the proper individuals. If he/she is unwilling to do so, there is contact information for the appropriate depts. in the aforementioned links,
I hope this information was useful. If it was, your feedback is greatly appreciated.