Canada study permit

[Funmi1]

Hello, I recently applied for a Canadian study permit and I was refused. The reason for refusal was that the officer wasn’t sure that I’d return at the end of my visit due to purpose of visit. I provided enough documents to support my application, acceptance letter, receipt of my first semester tuition fee which had already been paid for, I also stated that I would return at the end of my stay in my explanatory letter (which I actually intend to, i returned home after I completed my first degree in the UK and I also intend to do the same as I have future plans to invest in my home country). I don’t understand if I was refused because I applied to study a diploma course in Canada even though I already had a first degree in the UK. I would like to apply for masters directly but i don’t have the required grade for masters.

Please I need advice on what I need to do differently so my application won’t be refused again.