For start spiritual science is different from sciences we are already familiar with.
For physics, we have scales to measure weight/force etc…, for chemistry trough several procedures we can analyses the content of some element in some material. Science is a procedure that you repeat and results will be the same every time you repeat the experience.
5. Spiritism is the new science which has come to reveal to mankind, by means of irrefutable proofs, the existence and nature of the spiritual world and its relationship with the physical world. It appears not as something supernatural, but on the contrary, as one of the living and active forces of Nature, source of an immense number of phenomena which still today are not fully understood, and because of this they are relegated to the world of fantasy and miracles.
Spiritism is also a philosophy since study of fundamental problems related to the existence, knowledge, truth, the moral and aesthetic values
Spiritism is also a religion since it brings us closer to God, establishing a roadmap for our evolution in order to become perfect beings
Life after death, for us is easy to answer; yes there is life (in a different form) after death (from the material body). How can we know/prove? There is thousands and thousands of cases of reincarnation, this by itself shows that we continue live and come back to a new body to have new experiences towards our evolution. Past life therapy use this concept solve some psychological issues.
Other way to prove is by reason, why God created us for live just one life, how can you explain differences among us, God has preferences among all His children’s? This is absurd son reincarnation is the only possible answer to this equation!
More details you can find on below 5 books from Allan Kardec
Regarding your attempts to contact your mother, know that the "phone" rings in one direction only from there to here and not the other way around. Also your mother could not be “healthy” or prepared or (she / you) do not have the merit enough to have this blessing.