This is unfortunate and I am sorry to hear the travel from Milan was not spotless.
Where did you buy the original ticket, with SBB or DB?
Kindly note, the refund is not handled by SBB if the original ticket for Germany was not bought with SBB.
If you bought it with DB, you should contact DB to refund the original ticket while presenting the second ticket. In Switzerland you travelled on Interrail, hence on a different ticket. SBB is not liable for later connections.
As proof that you have taken the train from Milan (and therefore missed the connection), you have your Interrail journey log as well can you download a delay confirmation from SBB here:
Furthermore, if the delay was more than 1 hour, you may get a compensation from Interrail: https://www.interrail.eu/en/support/delay-compensation
Here are the passenger rights: