Edgar we need more information to understand the big picture for your problem. Blueberries are bog plants. Blueberries need pH of 5.5 to 6.0 max. 7.0 is too high.
I've just viewed your pictures. This blueberry is in a pot. Plants in pots have to have potting soil. Sterilized potting soil out of a bag. No water holding gimmicks no fertilizer added to that soil. Sterilized is the key. Is that pot filled with sterilized potting soil or garden soil?
From what I see, that plant needs NPK, a basic fertilizer. You said you are using fertilizer. What exactly are you using for fertilizer? I made up this little ditty; Less is best, more is death and none is dumb. Does that help? Please tell us what you are using for fertilizer, for soil. What are your plans for this shrub? Is this indoors or on a patio?
Ideally, this potted blueberry MIGHT flower and produce blueberries on a covered patio with pH adjusted soil (there are potting soils made for acid loving plants). Forget your blueberry thriving in doors. Have you guys been getting snow and freeze? Is this normal?
If you have a covered patio, take your plant out there for the day but make sure you bring it in at night. I have blueberries both in my greenhouse as well as outside the greenhouse. They are used to dormancy and cold.
Moving a plant from indoors to out of doors in the sun can kill plants. When a plant is set out of doors even on a covered patio it needs to be acclimated to temperature changes that don't happen indoors. You have to bring plants back indoors for the night. Moving plants from out of doors and direct sun to the indoors will also kill plants if not properly acclimated. More information, please. As soon as possible.