Ex help. What shall I do!? 🙈

So. Abit of a long one.

Kicked my ex out 7 years ago, for being a waste of space. Didn't contribute to the house, was crap with our son and didn't work. I worked nights and would have to get my mother to have our son, so I could sleep the next day, as his dad wouldn't look after him, even tho he was home.

So fast forward 7 years.

He has our boy every other weekend, although is late collecting on a Friday, and drops him home as early as he can on a Sunday. Normally resulting in my son having to come to work with me for abit. Luckily I'm self employed and my work allows him to do that.

I Have an amazing Fiancé, who adores my boy, and he does him. He does everything for him, as classes him as one of his son's (he has 2 of his own)

His dad is suppose to pay me maintance every month on the 25th.

Every month, without fail, I have to ask for it as he never pays it on time!

It's getting to the point where I would happily punch him, and that's not my personality, he just boils my blood so much!

He ignores my calls, even if I ring a few times.

Like this morning. Money hasn't been paid in, again. He's sending my calls to voicemail.

He doesn't even know why I'm ringing. Imagine if our boy was really poorly!!!

So, my question is.

Am I overreacting in getting so annoyed by it?

Or shall I do something about it and go down the official route to get the maintenance paid!?

Thanks in advanced xx