I'm sorry to hear that an interaction with the police force has been negative, but allow me to try and explain why this happened:
1. People seem to think that the police only provide good roleplay if they let a criminal go. This is not the case. We of course reward good roleplay, but roleplaying as police means that we give people tickets and we arrest criminals too.
2. The processed weed in your truck doesn't even remotely look like a flower and therefore a roleplay story that it's "flowers" or "weeds" (just another example) is very hard to make convincing. Especially because a police officer knows the difference between weed and regular plants very well.
=/=
3. What is 'denying roleplay' exactly in this situation? From what I can read the officers busted you doing weed, did not or partially believe your story and you received a punishment for having illegal narcotics with the intent to supply. Unless the officers' conduct during the situation was out of order (powergaming/metagaming or acting very unprofessional for example) I see nothing wrong.
4. Again, I don't know the details of your situation, but it seems to me that the officers requested you to put your hands up to detain you. You didn't comply and therefore were put in restraints with force. The punishment that you received is not even the maximum punishment (your truck could've been scrapped and you sent to prison) so I do think the officers took your roleplay into account when they made their decision.
4.1 It can seem that knocking you out and putting you in restraints is pretty shit and this is the number 1 complaint we get from rebels. However, if we don't put a suspect in restraints said person just uses that time to call his friends and it ends up with the police officers dead or taken hostage. Roleplay is a two way street.
5. If this server was 100% serious you wouldn't even had the chance to roleplay as you would be taken down by specialist units. There are plenty of things that aren't serious but are kept in the game for the sake of entertainment.