Ok, so you did a cal at 7. Then you did a cal at 4.
But when you subsequently tried to take a reading it did not read PH 4 as 4. Is that correct? What did it read at PH 4? What does it read at PH 7?
Doesn’t sound like it took the calibration.
Is there anything else that happened? E.g. the pen was unused for an extended period of time (e.g. 6 months)? Solution dried out? What is the storage solution that you are using and what does it read on the pen?