Any idea why my card was denied (Read details)

I was paying some bills. I had to pay my water bill. I go online, do the usual...and then see my card is denied! I check my number and expiration...its correct.I check my account...I have $175. The payment is $99.I call customer service and he says its either a newly activated card (3 years old...doubt thats that case). or insufficient funds (see above to disprove).The only thing I am thinking is a hold on my card due to gas? I got $5 dollars of gas and charged it to my debit card. They posted a $1 authorization charge...but I did not see any hold on it.Thanks!
      Answer1:Theres a difference between your ledger balance and available balance with a bank account. If your AVAILABLE balance cant cover the fuel and $99 bill, then the card will be denied.
      Answer2:You figured it out.When you buy gas on a debit card the station puts a $75 hold BEFORE you pump the gas. The hold is lifted once the charge goes through in about 1 or 2 working days./
      Answer3:The authorization $1 may have caused it. Cos sometimes do authorizations just to know the card works etc, and then the charges go through later. The CC co might then freeze the balance in case a large charge gets put throughAny chance theres something still pending that youve forgotten about? Other simple reasons I see cards denied are spelling error on address, middle initial missed out etc
      Answer4:Its due to the gas charge. Stations can put a hold on funds anywhere from $50 - $75 - this is posted on most gas station machines (all that I have seen, anyway). They will release the funds in 1 to 2 business days.However, my recommendation in the future to avoid this is this: When paying at the pump, process the debit card as a credit card. It wont post to your account as quickly as with debit, which can be a pain, but it will avoid the hold on your funds. Just be sure you know what your account balance is and remember to account for it!