When you see 'Refund Transfer" on your Notice Of Assessment (NOA), this means CRA has applied a part or all of the refund to another debt you owe. This is basically a "lien" on your refund and may have been taken by CRA for Income Tax, GST, CCB, or another Government Agency.
If you read through your NOA, it may say exactly where the amount held was sent. You can also check your CRA My Account, or call CRA at 1-800-959-8281