Call divert is off, but still the calls are getting diverted!

I have two phones, one I use for calling purposes (Mob1)and the other hand set has another working number (Mob2) but the WhatsApp number is of the Mob1.

So whatsapp number active is the same as of Mob1 and uses the internet which it gets from Mob2.

I give out Mob2 to only those from whom I don't want to recieve any calls. A call on Mob2 means ignore.

But something strange has been happening since last couple of months ... When someone calls on Mob2 (regular call).... I let the call end ... But then suddenly my Mob1 continues to ring when Mob2 ringing ends. The same call ringing carries on to my Mob1 even when the call divert is off.

How could this be happening? Is whatsapp the culprit here?

Has anyone else faced this issue? What is the solution?

Both the Sim cards are from Jio.