I find, if I buy a bag of frozen mixed veg, that the carrots are always rubbery and chewy. The other veg, peas, sweetcorn, green beans etc are always ok. I have never actually frozen any myself.
Often finding myself with a glut of carrots as I grow my own. What I do is peel and chop the carrots and then using a pot of boiling water, blanch the carrots for about a minute.
Remove them and rinse under cold water. Pat them dry with a tea towel and lay them on a tray before freezing. Make sure you loosen them on the tray after an hour or so. This will stop them sticking together, before you store them in an airtight bags.
Works every time ... we are still eating last years crop.