Procedure if received show cause notice from employer for resignation

I did travel for my employer in sep 17. After my travel/stay i submited bills for hotel. In Dec 17 employer is saying that my bill is not correct though money of bill is reimbursed to my account. I insisted I paid same amount which i mentioned. Employer is saying that they have bill with my signature. Hotel operator took my two signatures & it looks one is taken by employer which is less in amount.what should i do? Also main thing before my travel I insist employer to provide hotel for my travel but they deny due to there challenge. Also I was forced to go for this travel within short notice of 1 day. Due these two reason also i was not able to plan my travel in advance otherwise i will book hotel in advance & in genuine place. Now how should i deal with employer ,they are pressuring me to resign? Pl help