Ash Wednesday

So this morning Ex #1 and I were having a text message argument.

It is my fault it began, and I should know better. It may not appear 'stern' but I know exactly how he's be saying each and every word. Except for the last sentence.

I send Ex #1 a check every month to go towards the debt we acquired from breaking our lease, and to help with taxes on the house, because I believe it is the right thing for me to do. He expected to have my help when he planned for these costs, so I want to take care of my part.
I am really bad at deadlines though, and so I usually send it the last day of the month, or the first day of the next. So here it goes:

"Are you planning on sending February's check"

"yes"

"Okay. When? Today is March 1."

"I was planning on going today, actually. How much postage should I put on the SASE?" (So that he can send me my mail. We're all very professional.)

"Don't know. Post office will tell you." (This makes me unreasonably angry. I DON'T KNOW HOW MUCH MAIL THERE IS Ex #1!)

I am writing a message that says the above bold when another comes in:
"Send a big envelope, you have lots of mail." THANK YOU

a few seconds later:
"And don't forget to get your ashes."

WHAT??