Help I dont udnerstand one bit

Ok so heres my situation I was stuck at plat V and was stuck losing a lot so my mmr went to elo hell right. Then later I climbed all the way to plat 4 almost plat 3, this while winning 15 lp per win and losing about 21 per loss. and still riot mmr system had me at elo hell mmr. then again im climbing again have about 60-70% win rate in my last 20 games and was in promo to plat 3 again but still my mmr is considered elo hell wtf how do I fix it? Its almost impossible to climb when you win 15 and end up losing 21 every loss. Need HElp plz