？
Wait, was that seriously a debt collector?!
Literal
Surely-not real-[adverbially-に] debt [gen-の] dunning [copula-だった] [nominalizer-の]?
リアルに is internet-era slang where the loan adjective リアル ('real') is pressed into service as a casual intensifier adverb meaning 'seriously / actually / no joke.' The sentence-final の is the colloquial question marker, typically carrying a rising tone in speech (distinct from the nominalizer の inside clauses). 催促 is a relatively formal noun for 'pressing demand / dunning,' often paired with 借金 in debt-collection contexts.