src insurance aetna insurance company keeps refuseing to pay ligitmate claims lexington, Kentucky

I have been employed with Home depot full time for 6 years, and have had insurance through them the whole time.  In march of this year I took my social security and stayed with home depot part time. when I  went to part time my insurance changed from aetna to src, src is an aetna company that handles the part time insurance for home depot.    I was being treated by a doctor when I switched from full to part time, and gave the doctor all the information,  the doctor startes submitting bills under the new insurance that had been made after march, and  src keeps deniying to pay them because they say the bills occured after my coverage ended, or it was for an exhisting condition, 

I  contacted both the insurance company and the doctor, and was assured it would be paid after I got a letter from aetna stating I had coverage prior to march of this year, I did that,and the doctor resubmitted the bills again and once again was denied payment because they say I dont have coverage,  they are deducting the payments for the insurance from my pay check like  clock work, but still keep denying my claims,  the doctors are really getting fed up. they just want their money and if the insurance company isnt going to pay them, then they want it from me,, Iwill once again have to call src and try to get them to pay this claim,,