Product: Credit card

I had a gas credit card from Shell for several years, and I generally paid the full amount due, as the bills arrived. I paid my bill in XXXX of 2014, and thereafter received no new bills. 
Unexpectedly, in XXXX of 2014 Citibank XXXX the issuer ) began calling my residence, every day. My wife who is not well is home during the day, and asked me why Citibank was calling. I told her I did n't have any Citibank cards ( I did n't know Shell uses Citibank XXXX and it probably was solicitation. She would then pick up the phone and tell them to stop calling. They did not. 
Finally, Citibank called when I was home, and we spoke to a representative who demanded payment. It was explained that we had not received any billing and that we wanted an accounting as to what was allegedly owed, and the calls to stop. We were told they had the right to call every day. When the representative explained it was a Shell card, I thought back and believed there had been a purchase for about {$70.00} that may have not been paid due to no billing. In XXXX I estimated what I owed and sent {$100.00} to cover the bill, since I had still not received an accounting. The calls then stopped, but several weeks later re-commenced.I spoke to one of the callers, told her I protested the amount, that I had not received billing and requested a billing statement to enable me to determine what was allegedly due and when the charges were allegedly incurred. 
I heard nothing, and received nothing, in response but the phone calls continued. I then again spoke to one of the callers, explained the situation and again requested a statement that would detail the amounts owed and when they were incurred. Approximately 2 weeks later, I received a bill. This was the first time I was provided with a bill in months. It did not set forth the original debt, nor did it explain how I incurred late charges on bills that I did not receive, but merely set forth an amount allegedly due. 
Although I did not receive the full explanation I requested, I enclosed a check in the amount of {$120.00}, the amount represented to me as being the total amount due, under protest. I did not acknowledge that I owed this amount or any amount, but I merely wished the daily telephone calls to end. My wife, who is not well and at home during the day, is greatly disturbed by the calls. I also demanded, once again, a complete explanation of the billing that precipitated these charges. Since I did not receive the initial bill which led to this situation, I demanded a refund of all late charges paid, and that any negative reports affecting my credit be rectified. 
In response, I received a letter demanding that I speak with one of their representatives. I had already spoken to their representatives, and had not been able to get through to them that I did not owe any money, that I had been illegally billed for services that I had not incurred, and that I wanted the harassing phone calls to stop. Moreover, there was no reason to re-hash the situation with an employee who did not have the authority to resolve the issue, refund my unfairly charged " late fees '', and who had no authority to resolve the issue other than by demanding additional payment from me. 
Not only were my requests to stop the harassment, the illegal billing, to refund monies improperly billed, disregarded, but Citibank apparently continued to charge me XXXX what I can only assume are late fees ) without sending me any bills, and re-instituted its daily calls. I have ripped up my card, do not use Shell gas or any Shell products, and have not received any billing statements, so I could not have incurred any additional charges. 
I feel that this is not administrative oversight, but an intentionally calculated program to not send billing, and then charge late fees and penalties. Any assistance in resolving this matter would be greatly appreciated