Best answer by Transparent
Well firstly, I can't see how a new Direct Debit instruction could have been actioned within 3 hours. There are a number of checks to be made first because of issues like identity theft and anti-fraud legislation.
I'm more suspicious about the text which appears to have come from your bank. If it's a general notification message (which it is), then your bank wouldn't be asking you to reply.
Given that you don't even do online or Smart-phone banking, just how would your bank be set up to send you a text message?
It seems more likely to me that this text message wasn't sent by your bank. It could easily be a phishing scam, which seems all the more plausible to you because the scammer just happens to have chosen your particular bank on this occasion.
I get at least 20 messages each week from various banks, none of which I hold accounts with. The last thing I would do is to attempt to reply!