Curing an Overdue Hospital Bill Middleburg FL

I have medical bills and I have been paying monthly payments. But they turned my account over to a collector in spite of my regular monthly payments. Can they do this? Also, the collector is charging me interest. Do I have to pay the interest?
Martin Gottlieb Physician Billing
904-346-3088
4932 Sunbeam Rd
Jacksonville, FL
MDA Medical Billing Services
904-739-7248
4932 Sunbeam Road
Jacksonville, FL
Direct Physicians Billing Services Inc
954-626-0063
3601 West Commercial Blvd
Fort Lauderdale, FL
Advanced Medica
(407) 898-8382
3534 E Grant St
Orlando, FL
ACT Health Information Management
407-340-6282
P O Box 781645
Orlando, FL
Complete Medical Billing
(904) 783-1490
9253-1 Fish Rd
Jacksonville, FL
Global Medical Billing
(904) 880-2280
11534 E North Ride Cir
Jacksonville, FL
Advantis Healthcare Solutions
866-454-0612
7100 West Camino Real
Boca Raton, FL
Eclipse Practice Management Software
800-966-1462
15215 Technology Drive
Brooksville, FL
Candler Medical Billing
(305) 887-1330
10100 Nw 116th Way
Miami, FL