With no FPS information, its hard to say.
If you remember the FPS on the initial chrono session with 0.25g BB's, then pop in the figures in the top section.
In the bottom section, select 0.3g BB's and see the results of what the fps should be and if on second chrono there was any higher reading, then there was either something wrong :
With the chrono - like low battery, dirt, light, too bright
The way the chrono was used - in all chrono's I have used, 100mm must be between the barrel and the chron to prevent readings that are skewed.
The wrong setting was used for BB weight, something I have experimented with to show that the wrong setting skews true FPS.
https://www.zerooneairsoft.com/airsoft-fps-calculator
is a good tool to see this in action.
I hope you had a refund as you would be entitled to one with being told to leave the site, if you didn't, ask for one and when they respond, positively I hope, saves you then going to your bank or credit card to force a refund through taking out an indemnity against them. You also have trading standards that you can use as a way of validating your rights on this because more often than not, site rules and policy is quoted and that is not the law. To diminish your rights as a consumer is an offence for which trading standards can take action on the matter and they get a very nasty surprise, could even be fined harshly for unfair trading practices, such things have shut business down in the past.
I hope you get justice.