I want to leave home WITHOUT my Amex

My company makes us use the Amex corporate card for all business-related transactions, and this card is on personal liability.

Having an extra card in my nearly burst-out LV monogram purse is a chore, not only it is not widely accepted in many establishments, it gives me no perks but embarrassment. I used it for a business meal in KL but was denied after 3 tries by the cashier, alternatively I used my reliable MasterCard. I tried to use it again in HK at Crystal Jade, but it was not accepted; again I used my MC.

When I forgot to pay my Amex bill, I was charged a late payment fee of S$37.50 even though their officer promised to waive it off a month ago. Now Amex said there was no such "promise" recorded in their system but insisted I pay for the penalty. I was very upset as other banks willingly waived such penalty for me in all occasions, so why this exception at Amex? The officer simply apologized by saying "Sorry M'am but this is a company policy." repeatedly. It was clearly a scripted apology and his supervisor (Abigail) promised to revert with their "management's decision" on the waiver within 24 hours. Days passed and I heard nothing from them. I will not pay for the penalty though Amex said they would still impose 2% on the penalty every month. Will they even bother to sue me for not paying S$37.50?

What should I do? My company insisted that we use Amex for all business transactions, but I want to boycott it for good!