Suing is for spamming. Spamming is an unsolicited legitimate marketing call. Most of those calls originate in the US or are selling the products of US companies who hired them.
If appropriate laws existed, you could still put pressure on them. Something like "if your international partner sends more than X spam calls, you're responsible for them". The telco would have a choice of getting fined or dropping the interconnect / filtering that source. On the other side, the telco in Bangalore doesn't want to lose the ability to handle calls to the US, so starts monitoring itself.