Does BC/BS of Arkansas have to cover pre-existing conditions if I had coverage through BC/BS of Iowa since beg?

of year through husbands job. he lost his job in August which I then had to switch to my employer health plan. We actually had both insurances for2 months. They are denying coverage for dr appointments and tests that I had after I got there insurance saying they are preexisting which some are not. I have submitted certificate of credible coverage which they accepted and approved. I'm tired of fighting with them almost daily should I contact a lawyer or what should I do to get them to pay.?