[mothered]

Where is the limit? 10k, 20k

There are no hard and fast rules.

Obviously the greater the value, the more attention It will attract which may lead to a lengthy process.

And how often can you submit this to the bank...every 6 months...every 12 months?

To be on the safe side, once every 12-18 months.

That's on the grounds you're hitting chargebacks on a long-term basis.