Why are you offering a partial refund? To who ? I cannot see 1000 pens sold in one transaction.
If they have paid you outside an eBay listing, this is firmly against the rules and could get you a ban from selling.
Talking of bans, you need to take a look at your seller dashboard, you may be close to a selling ban because if all those negatives you received for non delivery of items, resulted in the buyer escalating the case, it would give you very damaging defects, it does not take many to close a new seller's account down permanently.
Whilst I understand the situation in your Country, and of course it's worldwide, if it is the Covid crisis bringing about late or non delivery you may wish to adjust your estimated delivery times on your listings, or just for the time being , until we have a more sane world, sell only within your own country, if your postal system internally is proving reliable.
