Ds123 wrote:

How can I terminate my membership? Noone wants to tell me...

I took this from the Terms of Service.

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4. TERMINATION
Either you or the BYOND Staff has the right to terminate your BYOND Membership at any time.

If your Membership is terminated by yourself or the BYOND Staff, there is no obligation for a refund of any amount you have paid for the membership. In the event of termination, the BYOND Staff will determine whether you receive a partial, full, or no refund on your membership.

The BYOND Staff takes BYOND Membership seriously, and wishes to provide you as much leeway as reasonable to allow you to use your BYOND Member site as you will, within the bounds of being a good citizen in this exciting community.
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Usually, users will allow the time to run out if they no longer need their membership. So beware, you may not receive a refund upon termination. Though, if you must terminate it for a specific reason, try using the support form.