I'm afraid you have to make a choice between the plant and the pot, if its narrower at the top than in the middle. It's next to impossible to get any of the plant out once its potbound, though you could try with a sharp breadknife to hack bits out until you can get the rest removed. Not sure any of the plant will survive the process though.

The only thing that type of pot is good for really is empty, for pure decoration, or to grow annual plants only, which you'll be binning after six months.

yes the bread knife, pruning saw to cut bits off is the only option or break the pot. sections that have decent roots coming from a growing point will survive but its unlikely to flower for some time. [2-3 years].