Advice please

I had a myreen(not sure of spelling) coil fitted nearly 2 years ago to help with extremely heavy periods and periods practically stopped, which was great.  However, in recent months they seem to have started again and gradually getting heavier.  Even had a couple bleed throughs at work this last week.  Anyway, just had a bath and four huge clots have come away, one size of palm of my hand.  Surely that can't be right??  Can these could just stop working??