What Causes Extreme Pain While Removing Mirena Coil?

Doctor tried o remove mirena coil and located strings. However unable to remove due to extreme pain when tugging on strings. A pain I can only liken to Labour. I have a decent tolerance to pain as I went through most of my labour without pain relief so why is it proving extremely painful to remove Iud? I found having it fiitted uncomfortable but trying to remove was unbearable and its still there!