£15.00 başına ayl Ödüyorum. I pay £15.00 per month (referring to my mobile phone bill). Thank you

 Aylık £15.00 ödüyorum. Her ay £15.00 ödüyorum.

Warg thanks

Ceketeni unuttu. He´s forgotten his jacket/coat. Thanks

Ceketini unuttu. Except one character, your translation and syntax are correct

 Just curiosity...which is more proper to use: leave or forget?

Or both are equally possible?

He forgot his jacket (in the train)

He left his jacket (in the train)

 He forgot his jacket: it was definitely a mistake. He meant to bring it, and forgot it.

He left his jacket: may be a mistake, or he may have deliberately left it. In your example (on the train) it seems like an accident, but "He left his jacket at home" could be deliberate because he knew the sun was shining and he didn´t want to have to carry it.

e.g. If some asks "Where is your mum?"

"I left my mum at home." as a reply means she didn´t want to come, so I left her at home doing other things.

"I forgot my mum!" is a panic reply, and I know I will be in trouble when I get home!!!!

 Thank you Marionin