If the NIP-05 part contains 'mostr.pub', that may not be the account you created on Nostr, as it is a kind of mirror account for ActivityPub-type accounts.
Maybe you have an account on Type.Social server and the account snagged matype_at_typo.social@mostr.pub is a mirror of it. 

 yes, i have my account on typo.social
i mean, i've created nostr account before( https://njump.me/nprofile1qqs8dxcz6uquxgcga57mkeftveegr3lpe6jvupc7zekkccwlmdrrtuqpz4mhxue69uhhyetvv9ujumt0wd68ytnsw43qhhdt0a ), and matype_at_typo.social@mostr.pub is now tied to the account, so i'd like to deactivate it 

 It is probably not possible to deactivate the mostr account and the NIP-05 with "@mostr.pub".
Mostr account is automatically generated and a NIP-05 with "@mostr.pub" is set up at the same time. 

 isn't it? 😭 thanks a lot for letting me know!