Tax question

So my husband is self employed and did not take care of his taxes until July. He was told by his accountant that he automatically files extensions for his clients. So he gets the taxes done, mails the check and done. Well in September we receive a letter in the mail stating we owe a penalty. I contact the account and send the paperwork and he said he will take care of it. A month goes by, I receive another letter. He says he never received the first email so I resend everything. Just received another letter in the mail today saying we owe the penalty. Obviously the accountant did not take care of any of this. Should I just pay it at this point? I tried taking care of it with the accountant but that is getting me no where