Hold up. You were logging into multiple accounts on the same IP without using a VPN? Were you not even using proxies and switching between them as you went?
Even if a lot of them were sides and not shells/mains, that's definitely suspicious and I'm not surprised if they froze over monitoring IP and location activity.
Buying things from user shops isn't exactly strange, even on sides, since assets such as NP or items transferred from a main account is fair game to be used on side accounts. But multi-accounting or logging into tons of accounts on the same IP is definitely "strange", and TNT in all their freeze-happy glory can and will jump on that when they notice it.
Definitely invest in elite proxies and/or a VPN if you continue to multi-account.