Metaphysical solipsism cannot be true because the burden of proof it assumes is impossible to satisfy. Yes proof is knowledge.
*Before you lay a completeness and/or incompleteness argument on me take note we don't know if axioms of ZFC leads to a contradiction somewhere, but we don't assert it ZFC is absolutely true. The solipsist is asserting an absolute truth.
"metaphysical solipsists maintain that the self is the only existing reality and that all other reality, including the external world and other persons, are representations of that self, and have no independent existence"--Wikipedia
You can't prove all of what you are without causing an infinite regress. So it is unreasonable to hold that position. While you may insist it could be true and you not know it, if your mind is not aware of everything your mind can't be everything. If everything was your mind supposedly you could prove it.
Epistemological solipsism is conditionally false if we assume it isn't an umbrella statement speaking to limitations of all persons when it includes " external world is regarded as an unresolvable question". As a materialist I concede "conditionally false" because some of us are not able to follow my technique for proving and external world for a reason such as brain injury.
Here is my technique. Deny all your beliefs and assumptions, and if anything remains your mind cannot be foundation of reality, thus external reality.
As for Methodological solipsism it is too wishy-washy if I go by the wikipedia entry.