Unwanted / unsolicited OTPs coming to my number

I've been getting OTP's sent to my number - with no way supp**** to communicate with PayU to let them know that I'm either receiving OTP's erroneously or that this is some form of *****. Their website has a chatbot, a form for businesses to fill in, but now way to contact the technical dept, except you can write them... by snailmail. Who on gods green earth still uses that? Makes me think they don't want to be bothered on purpose.