I recall having the same issue iirc, I believe there's another requirement before she gets back to you. Might be you have to learn lockpicking? The phone messages to her might give insight. Sorry, I can't recall exactly what I did to fix it but it should be possible.
As I said before, there's no condition for Mercedes to text you back once you text her you have the bank receipt.
Let me get a bit technician here. The code that sets the condition for Mercedes' message is this:
Code:
if (ch59.tim > 55 or ch60.tim > 55) and not "xx61" in mr.chat and h > 13 and h < 23:
This basically means that:
- if more than 55 minutes have passed since you texted Mercedes with one of the messages you as a player can sent to her,
- if Mercedes has not texted you back with her next message and
- if it is between 2 and 10 pm
you will get a new Mercedes message. There's no possible bug here: as long as you fulfill the three requirements above, you must get her message.
About spamming the button to fast forward 4 or 7 hours: there is the possibility that if you do that, you will skip certain events related with the smartphone that take place in a time span less than 4 or 7 hours. This Mercedes thing is not the case but still, I'll re-write the code a bit so that this can't occurr.