Your reputation with this site is essentially no more than internet points. Your work, your experience, and your ability stays with you.
The ultimate goal of any agency-type business is to take the maximum amount of money from their clients while doing the least possible amount of work for them. If the clients feel locked-in (as you do), that's brilliant for them, because they can abuse you in this way and they know you won't change your behaviour apart from grumbling on some forum.
Although others are suggesting you use a competitor, I think you should consider whether this is a business model you want to support in the future.
Yes, but if your whole reputation is tied to a single site, you're doing something very wrong. Building an entire freelance business around a single site, never doing any open source work, never networking, and never doing any pro bono work for local charities is a very bad business practice.
The ultimate goal of any agency-type business is to take the maximum amount of money from their clients while doing the least possible amount of work for them. If the clients feel locked-in (as you do), that's brilliant for them, because they can abuse you in this way and they know you won't change your behaviour apart from grumbling on some forum.
Although others are suggesting you use a competitor, I think you should consider whether this is a business model you want to support in the future.