Are there any circumstances in which I can appeal LTD after the number of days Aetna gives you to appeal?

My question: is there any circumstances in which I can appeal LTD after the number of days Aetna gives you to appeal a denial? I was approved on Aetna STD claim, I paid for and approved on a Aetna LTD claim that work paid for. I was on them for 2 years when the LTD needed a second Dr to say I’m disabled and that I didn’t turn in my forms by the due date so they stopped payments, was denied. They had April as the due date in the form letter. I called and she said it was a typo and the due date remained which was Feb and there was nothing I could do. That was Feb 2018. I have since been approved for SSDI and Aetna STD, that switched to LTD after a year I still receive. I had to call Aetna to ask questions because I recieved my SSDI award letter and I asked about that claim and she told me that I should have talked to her supervisor and not “just sit on my hands and do nothing”. I tried to explain to her what happened and she said if I have more than 1 letter w the typo that I should do something however, this is a year later. I was not aware there was anything I could do. The claim manager never told me I could appeal, she told me there was nothing I could do even if it was a typo. Can you still appeal after the appeal deadline has expired in this kind of circumstance? I didn’t understand appeals and I feel the claim manager lied to me about the typos. I do have several letters with that “typo”. She also never told me about appealing the decision.