Why sometimes I can't cancel my order at the market?

I am trying to cancel my other so I can change the value of my order, everything goes well but my order is still up (not cancelled).

What makes it happens?

How can I get a actual cancellation of my order?

I get very nervous with that. I have already lost some Steem because of no cancellation of my order. I am not even close to the actual steem price, it is not a case of trying to cancel an eminent order that actually have already happened. I am trying to buy Steem on a price at least 0.08 of diference. and the market is pretty close on prices now.

Could anyone help me with answers?

Many thanks in advance for your understanding and cooperation.