HCG after m/c?

Keighlen
So I went to the ER the other night because I was bleeding and cramping and the doc told me they believed I was miscarrying. So we had a few days to accept I had a miscarriage and move on. My primary care provider told me she wanted to monitor my hcg levels until they got to 0. And within two days my levels doubled and my cervix is still closed. Has this happened to anyone else after m/c? Is it possible the doctor was mistaken and I still have a baby in there?