Do you have appraisals by your manager? That's the way for him/her to address your attributes and shortcomings formally but also the way that you bring up matters concerning your working practice. If you're advised to manage your time better, maybe they should offer you a time management course?

Another option is to fail some task (no-one likes to do that), preferably one of the sales tasks and, when there's a "post mortem" to investigate why, then you show them documentary evidence of what you've been doing, time taken etc. compared with your job specification.

If they insist on using you in this way, I suppose there's always an option of invoking a Union (I don't know if you have such a body to take up such a grievance) or you could move on elsewhere.