The only way to address the problem is to contact Xfinity.
Payment may have "crossed in the mail". Meaning your service was cut off after you mailed payment but before Xfinity received that payment.
Please be aware that it is very possible that your payment never got to Xfinity. Or was credited to some other customer.
That just happened to us a few months ago. Check literally got lost somewhere and we had to cancel that check and hand deliver a new check.
Which had to clear the bank before our service got cut off.
Once your account is back in good standing then your public hotspot should return.
In the meantime get ready to provide "proof of payment" to Xfinity. E.g. a cancelled check, cash reciept, or some proof of...