You are using a string as a key in your hash map instead of a regular expression object.
Here is the correct hash map declaration:

file_types = {
    /camt.053.001/ => 'camt053',
    /camt.052.001/ => 'camt052',
    /"Auftragskonto";"Buchungstag";"Valutadatum";/ => 'SpK'
}