Matt is correct, Muhammed. It sounds like your teacher had a typo (it happens to the best of us!). Your sentence should read 'Old people who have been used to going into the bank to MAKE transactions find it difficult to change this habit'. We usually MAKE transactions. You could also put 'used to' in the present simple with little change in meaning, so: 'Old people who are used to going to/into the bank...'. It just makes their familiarity sound more current. Hope this helps!

Thanks Matt for the comment, actually the sentence is written by a British IELTS teacher, and I found it difficult to digest the extra "to".

The usage is correct, but you need to take away the word "to" after going. It should be "Old people who have been going into the bank to do transactions...."