Cello — I am complaining about cello technotip pen(black & blue ink)

I have been regular customer of cello technotip pen.But lately i’ve been facing some issue that the pen is not working after 1 week o[censored]se.I bought the same pen from another stores but still face the same issue(4 times)This made me helpless during my exam also.i hope you will consider your dearer customer and will take necessary actions.