Aetna and UConn Health are locked in a bitter fight over reimbursement rates, and nearly 15,000 patients could lose in-network access if there’s no deal by Sunday. UConn Health is blasting Aetna with billboards urging higher payments, saying low commercial rates force the system to expand just to survive. Aetna accuses the health system of trying to become one of the priciest in New England. Some appointments are already being canceled as both sides dig in, leaving patients caught in the middle.