Listen to this and see if you can here the characters at each of the speeds. If you can not, then you may have learned the code using visual aids like stupid charts, etc. You must undo the damage immediately. So listen to this over and over until you can recognize the characters by sound and sound alone. Not by replaying in your mind.
Immediate recognition is absolutely necessary.
Please also note. These characters are generated with rise and fall times that don't thump. I use only earphones when listening to morse code for many reasons too numerous to list here, but the most important is that in using speakers sound reflections from walls will cause problems especially at the higher speeds. Also protect your ears at all costs. Use the lowest volume you can.